Bell 
 EL Dorado, Arkansas oil and gas field*
 
 
 THE LIBRARY 
 
 OF 
 
 THE UNIVERSITY 
 OF CALIFORNIA 
 
 LOS ANGELES 
 
 The RALPH D. REED LIBRARY 
 
 O 
 
 DEPARTMENT OF GEOLOGY 
 
 UNIVERSITY OF CALIFORNIA 
 
 LOS ANGELES, CALIF.
 
 STATE OF ARKANSAS 
 
 Bureau of Mines, Manufactures and Agriculture 
 JIM G. FERGUSON, Commissioner 
 
 The 
 
 El Dorado, Arkansas 
 Oil and Gas Field 
 
 Geological Outline 
 
 Operation Methods 
 
 Conservation 
 
 By 
 
 H. W. Bell and J. B. Kerr of 
 the U. S. Bureau of Mines 
 
 Published Under the 
 Joint Auspices of the 
 
 UNITED STATES BUREAU OF MINES, THE UNITED STATES GEOLOGI- 
 CAL SURVEY, THE UNIVERSITY OF ARKANSAS AND 
 THE STATE BUREAU OF MINES, MANUFAC- 
 TURES AND AGRICULTURE 
 
 LITTLE ROCK, ARKANSAS 
 1922
 
 CONTENTS 
 
 PART I 
 U. S. BUREAU OF MINES 
 
 Page 
 
 Introduction 7 
 
 Acknowledgments . 7 
 
 History of Development 8 
 
 First Wells , 8 
 
 Acreage and Oil Prices 11 
 
 Storage and Marketing Facilities 11 
 
 State Conservation Commission 12 
 
 Co-operation by U. S. Bureau of Mines 12 
 
 Drilling Methods 13 
 
 Equipment arid Power 13 
 
 Casing Program 14 
 
 Testing Formations 14 
 
 Completing Wells 18 
 
 Labor Conditions 20 
 
 Drilling Costs 22 
 
 Water Conditions 22 
 
 Amount Water Produced 22 
 
 Harmful Effects of Water 22 
 
 Source of Water 23 
 
 Analyses of Underground Waters in El Dorado Field 31 
 
 Association of Oil and Water 33 
 
 Use of Cement 34 
 
 Handling of Cement 40 
 
 Abandonment of Wells 41 
 
 Protection in Case of Deeper Production 43 
 
 Production Record 44 
 
 Oil Produced, Proven Acreage, Well Spacing 44 
 
 Quality of Oil 48 
 
 Surface Wastage 48 
 
 Production of Gas 51 
 
 Production Decline Curves for Oil Wells 53 
 
 Production Methods 1 55 
 
 Safety Devices 56 
 
 Oil, Gas and Water Separators 58 
 
 Dehydration 60 
 
 Natural Gas Gasoline 62 
 
 Types of Oil Well Pumps 64 
 
 Oil Recovery from Unconsolidated Sands 64 
 
 Perforated Liners and Screen Pipe 65 
 
 Flow Oil through Tubing 66 
 
 Air Lifts for Raising Oil 66 
 
 Vacuum Pumping 67 
 
 Power for Pumping 67 
 
 Counterbalances and Tail Pumps 68 
 
 Conclusion ... Kg
 
 Librarj 
 TN 
 
 CONTENTS 
 
 ILLUSTRATIONS 
 
 Page 
 
 Frontispiece. Airplane View of El Dorado Oil Field 6 
 
 Plate A. Map of El Dorado Oil Field Pocket 
 
 Plate I. Busey Well (shown in foreground), Section 31-17-15, 
 
 the first oil well completed in the El Dorado Field. 
 Well began producing January 10, 1921. Photo taken 
 
 after abandonment of well 9 
 
 Plate II. Bailing down to bring in well. Connections made for 
 
 Flowing Well 17 
 
 Plate III. Water Infiltration Possibilities and Method of Cement- 
 ing Bottom of Hole under Pressure...... Pocket 
 
 Plate IV. Generalized Sections, Showing Approximate Thick- 
 ness of Oil-Bearing Strata and Association of Oil and 
 
 Water Pocket 
 
 Plate V. Diagrammatic Northeasternly Cross Section in Nor- , 
 
 them Part of El Dorado Oil Field Pocket 
 
 Plate VI. Diagrammatic Easterly Cross Section in Southern 
 
 Part of El Dorado Field Pocket 
 
 Plate VII. North-South Diagrammatic Composite Section, Show- 
 ing Character of Strata Comprising the Oil Zone and 
 
 adjacent to it '. Pocket 
 
 Plate VIII. Preparing to Cement Well under Pressure in Bottom. 
 Arkansas Natural Gas Co., Wood No. 199, Section 
 
 20-18-15 38 
 
 Plate IX. Intensive Drilling near South Boundary of Section 17- 
 
 18-15. Shows Open Earthen Sump for Oil Storage 45 
 
 Plate X. Estimated Oil Production of Average Wells of Field.. Pocket 
 
 Plate XI. Waste of Oil by Storage in Earthen Sump 50 
 
 Plate XII. A 55,000-barrel Steel Tank on the Standard Oil Tank 
 Farm. Shows Portion of Adequate Fire Wall which 
 
 Centers the Tank in a Closed Basin 51 
 
 Plate XIII. Average Production Decline Curve Pocket 
 
 Plate XIV. A Steel Choke Worn by Passage of Sand with Oil 55 
 
 Plate XV. "Christmas Tree" Equipment of about Average Design 56 
 
 Plate XVI. Discharge of Water and Some Oil from Separator. 
 Gas and Oil Risers at Ends of Separator not Shown, 
 Some Oil being Wasted with the Water through the 
 
 Bleeders 59 
 
 Plate XVII. Discharge of Water from Separator, Clear Water being 
 
 Discharged from the Bleeders.. 59 
 
 Plate VXIII. The Two-Unit Electric Dehydrator on the Hearin Lease 
 
 of the Humble Oil Company 61 
 
 FIGURES 
 
 Fig. 1. Cable Tool Lubricator for High Pressure Wells 21 
 
 Fig. 2. Dump Bailer 37 
 
 Fig. 3. Field Production Curves Pocket 
 
 Fig. 4. Gas-Oil-Water Separator 57 
 
 Fig. 5. Sand Trap Used in Some of the Pumping Weils 63 
 
 TABLES 
 
 Table 1. Production, Deliveries, and Stocks of Oil, and Dry 
 
 Holes, and Gas Wells of El Dorado Oil Field, January 
 
 to October, 1921 10 
 
 Table 2. Collapsing Pressure and Capacities Pocket 
 
 Table 3. Table of Capacities between Casing of Different Sizes 
 
 and Weights 15 
 
 Table 4. Water Analyses of El Dorado Field 65 
 
 Table 5 Analysis of El Dorado, Arkansas, Crude Oil 49 
 
 Table 6. Decline in Gas Pressure and Production of Some of 
 
 the Wells of El Dorado. 52 
 
 Table 7. Estimated Future and Ultimate Production for an Av- 
 erage Well in the El Dorado Field 53 
 
 76309O
 
 CONTENTS 
 
 PART II 
 
 U. S. GEOLOGICAL SURVEY 
 El Dorado Oil Field Page 
 
 Discovery and Development 71 
 
 Studies of the Geology 71 
 
 Structure of the Field 71 
 
 How the Pool Was Formed 74 
 
 Oil and Gas above the Principal "Pay" Sand 75 
 
 Possible Extension of the Field 75 
 
 Possibilities of Similar Fields Elsewhere in Southern Arkansas 75 
 
 Description of Producing Beds 76 
 
 Methods Used in Constructing the Map 76 
 
 Character of the Oil 77 
 
 Some Mistakes in Drilling Methods 79 
 
 Elevations of Nacatoch Sands 78 
 
 Ages, Relative Positions and Thickness of Formations Encoun- 
 tered in Drilling in the El Dorado Field 79 
 
 Yegua ( ?) Formation 79 
 
 St. Maurice Formation 79 
 
 Wilcox Formation 80 
 
 Midway Formation 80 
 
 Arkadelphian Clay 80 
 
 Nacatoch Sand 80 
 
 Marlbrook Marl 80 
 
 Annona Tongue of the Austin Chalk (?) 81 
 
 Brownstown Marl 81 
 
 Blossom ( ?) Sand 81 
 
 Eagle Ford (?) Clay 81 
 
 Record of Deep a Well Near El Dorado 
 
 Geologic Structure in the Region 
 
 MAPS 
 
 Structure of Northern Part of El Dorado Field 72 
 
 Cross Section of Southern Arkansas Pocket 
 
 PART III 
 
 DATA BY J. A. BRAKE, 
 State Oil and Gas Inspector 
 
 Extensions of El Dorado Field north, east and west 87 
 
 Log of Murphy No. 1 Well 87 
 
 Log of Frazier Well 89 
 
 ILLUSTRATIONS 
 Burning Well by Day and by Night 88-90
 
 Fo 
 
 rewor 
 
 IN THE absence of a State Geological Survey, and without an appropria- 
 tion of any kind for research work, the Bureau of Mines, Manufactures 
 and Agriculture is fortunate in being able to give to the public this re- 
 port on the petroleum and natural gas resources of the El Dorado field, 
 together with the timely recommendations embraced therein for the guid- 
 ance of drilling operations and for the conservation of these important 
 minerals. 
 
 Publication of this material has been made possible by a prompt and 
 cordial response to the State's call for co-operation upon the United States 
 Bureau of Mines and by substantial aid from the University of Arkansas 
 and the State Banking Department. The report also includes timely data 
 on the geological features of the field previously issued in press bulletins 
 by the United States Geological Survey. 
 
 It has been difficult to work out some of the problems met with, both 
 in a study of the geology of the region and in the methods of drilling and 
 controlling the wells, and the report has been delayed to await the settle- 
 ment of some of these perplexing questions. It has been especially difficult 
 to correlate the well logs, necessary to a correct understanding of the struc- 
 ture, due chiefly to the use of rotary equipment, which gives up few fossils. 
 The report was held up some three months awaiting the geologic matter. 
 
 With this explanation, I am pleased to give the public the report as 
 furnished by the co-operating agencies of the Federal Government, without 
 change. The expense of publication is defrayed wholly by this depart- 
 ment, out of its limited printing fund. A copy of the report may be obtained 
 free by any citizen of Arkansas or person residing outside of the state who 
 is actually interested in oil and gas development. 
 
 Commissioner of Mines, Manufactures and Agriculture. 
 JOHN C. SMALL, 
 
 Editor of Publications.
 
 Drilling and Production 
 
 H. W. BELL* AND J. B. KERRf 
 
 The United States Geological Survey has compiled a report dealing 
 with the geologic features, the accumulation of oil and gas and the possi- 
 bilities of extending the producing area of the El Dorado Oil Field, Arkan- 
 sas. The engineers of the Bureau of Mines have made a study and prepared 
 the following data on methods of drilling and production. It is believed 
 that if some of the suggestions in this report are adopted, the operator will 
 enjoy a greater profit. These suggestions are primarily based upon the prin- 
 ciples of the conservation of oil and gas. 
 
 The El Dorado Oil Field, Arkansas, has developed rapidly since January 
 10, 1921, when the first well that produced commercial quantities of oil was 
 completed. The low prices for oil and lack of adequate pipe lines and tank- 
 age in the earlier months, did not apparently retard the rate of development 
 to any extent. Up to November 1, 1921, the field had produced approx- 
 imately 10,000,000 barrels of oil from a proven oil area of about 4,825 acres, 
 which was an average of 2,150 barrels to the acre. 
 
 The maximum daily production of the field was about 77,000 barrels, 
 which occurred for a few days in August, 1921. The production decreased 
 to about 44,000 barrels per day by the middle of October, 1921. Since 
 August, 1921, producing wells were completed at the average rate of about 
 twenty per week for three months. By the end of October, 1921, about 460 
 commercial oil wells had been completed. The initial productions of the 
 oil wells ranged from only a few barrels to 15,000 barrels of oil per day and 
 the gas wells up to a maximum of about 40,000,000 cubic feet of gas per 
 day. Unfortunately, some of the wells have 'been inefficiently handled, 
 which has resulted in considerable waste. 
 
 The El Dorado field furnished the first commercial production of oil 
 in the State of Arkansas. Gas has been produced since about 1905 in the 
 Fort Smith gas field, which lies near the Oklahoma line and some 175 miles 
 northwest of El Dorado. Because of this gas production, the Arkansas Leg- 
 islature passed an Act in 1917 which dealt with the conservation of oil and 
 gas. The situation for El Dorado was therefore unique, in that the first 
 oil production of the State was immediately subject to the regulations of 
 a conservation commission. 
 
 The excessive production of sand with the oil has been the source of 
 much trouble to the operators and has caused them to give considerable 
 attention to the handling of this problem. 
 
 The excessive production of water in some areas has curtailed or 
 stopped the production of oil and gas. Several factors have contributed to 
 a more rapid increase in water production than was necessary. One object 
 of this" report is to indicate the harmful effect of water and to discuss the 
 most effective methods of excluding the water and operating the properties. 
 
 ACKNOWLEDGMENTS 
 
 This report was prepared at the request of and in co-operation with the 
 State of Arkansas, whose financial aid made the work possible. The Univer- 
 sity of Arkansas, the Arkansas Bureau of Mines, Manufacture and Agricul- 
 ture, and the State Banking Department provided funds. 
 
 The writers wish to acknowledge the assistance of the respective de- 
 partment chiefs, Dr. J. C. Futrall, Jim G. Ferugson and W. T. Maxwell. 
 Assistance was also given by Messrs. J. A. Brake, State Oil and Gas In- 
 spector; E. E. Winger, Oil and Gas Inspector and formerly expert driller 
 for the Bureau of Mines, and John J. Doyle of the Margay Oil Company. 
 
 The operators and others familiar with local conditions kindly furnished 
 logs of wells, production records and miscellaneous information. Messrs. 
 
 *BelI, H. W '., Petroleum Engineer, U. S. Bureau of Mines. 
 
 fKerr, J. B., Assistant Petroleum Technologist, U. S. Bureau of Mines.
 
 EL DORADO. ARK., OIL AND GAS FIELD 
 
 L. W. Mosburg and H. W. Hoots of the U. S. Geological Survey co-operated 
 in the collection of data. The El Dorado Chamber of Commerce furnished 
 space and equipment for field headquarters. 
 
 Thanks are extended to the following, who co-operated in the prepara- 
 tion of the report: Eugene Holman, P. H. Walber, D. B. Harris and J. L. 
 Finley of the Humble Oil & Refining Company; J. E. Todd, V. C. Megarity, 
 W. C. O'Ferrell, S. C. Strathers, F. Ray McGrew, F. B. Bimmel, and Howard 
 Murphy, of the Standard Oil Company of Louisiana; E. J. Raisch of the 
 Federal Petroleum Company; H. Gandy and J. W. Westmoreland, of Gulf 
 Refining Company; J. H. Mann and C. M. Palmer, of the Mann Oil Com- 
 pany and Imperial Oil Company; J. F. Wright, oil lease superintendent and 
 deputy conservation agent; Roy Wilson, H. S. McGeath, E. D. Holcomb, of 
 the Magnolia Petroleum Company; A. J. Jones, Kansas Gulf Company; E. E. 
 Windsor Southwestern Oil Company; Bradford Hearn, Shreveport Pro- 
 ducing and Refining Company; Elton Rhine and J. T. Lord, of the Amerada 
 Petroleum Company; J. B. Sowell and W. M. Coats, of the El Dorado Natu- 
 ral Gas Company; George M. Sonfield and Jos. Parks, Sun Company; J. O. 
 Nelson, J. P. Smoots, Arkansas Natural Gas Company; Elaine Johnston, 
 White Oil Corporation; George McPherson, operator; H. W. Holland, El Do- 
 rado Petroleum Company; Charles Carter, drilling contractor; Ed Hollyfield 
 of Hollyfield et al.; C. H. Kampeter of Parry Oil Company; D. J. & J. H. 
 Johnson of Johnson Drilling Company; H. C. Eddy of Petroleum Rectifying 
 Company; A. J. Graff, of Constantin Refining Company; H. N. Spofford, 
 of Gladys Belle Oil Company; A. K. Gordon of Louisiana Oil & Refining 
 Company; G. M. LeGrande of the Michigan-Arkansas Oil Company; C. E. 
 Larder, of Sinclair Oil Syndicate. 
 
 The work was carried on under the general direction of Mr. A. W. 
 Ambrose, Chief Petroleum Technologist of the Bureau of Mines. T. E. 
 Swigart offered many helpful suggestions in the preparation of the manu- 
 script, and W. W. Cutler assisted in the construction and preparation of 
 the production declines and appraisal curves and data. 
 
 The writers wish to express appreciation for help and criticism to the 
 following members of the Bureau of Mines; R. Van A. Mills, W. W. Scott, 
 W. H. Strang, H. H. Hill, J. H. Wiggins and W. B. Lerch. 
 
 History of Development 
 
 First Wells: 
 
 The first successful well in the El Dorado field was a gas well brought 
 in by the Constantin Oil & Refining Company, in Section 12-18-16 (see Map, 
 Plate A), in April, 1920. This gasser had an initial open flow capacity of 
 about 30,000,000 cubic feet per day and a rock pressure of 960 pounds per 
 square inch. Several other gas wells were drilled in Section 12 and in the 
 adjoining Section 1. Oil did not begin to appear in these wells in important 
 quantities for some months and only shortly before the oil boom was 
 initiated by the advent of the Busey well did they show oil at all. These 
 first gas wells did not attract much attention from the public, probably 
 because the Fort Smith gas field had produced no oil in fifteen years, and 
 it was the general impression that there was little likelihood of- finding oil 
 at El Dorado. 
 
 During the latter part of August, 1920. drilling operations were started 
 on the Armstrong farm in the NW*4 of Section 31-17-15 by Mitchell and 
 Bonham. Considerable mechanical difficulty and financial trouble were 
 encountered in drilling this well and it has been reported that the hole was 
 twice abandoned and the derrick skidded a short distance for a fresh start. 
 Dr. S. T. Busey became interested in the well and assisted in pushing the 
 work to a successful conclusion. The well came in January 10, 1921, with 
 a large amount of gas and an oil production probably exceeding 5,000 bar- 
 rels per day. This well has since been known as the Busey well. 
 
 The Busey well was drilled with rotary tools and that practice has 
 been followed for all other wells in the field. In a few instances, wells have 
 been finished with cable tools. Adequate precautions were not taken and 
 the Busey well blew wild for some time. The ground and foliage were 
 sprayed with oil for a considerable area about the derrick. After about 
 fifteen days blowing wild, water began to appear and the fluid turned to a 
 brownish color. Efforts to control the well were unsuccessful. The water 
 increased rapidly until the oil and gas were completely choked off, limiting 
 the well's productive life to about forty-five days.
 
 EL DORADO, ARK.. OIL AND CAS FIELD 9 
 
 In drilling the Busey well, sand and lignite were logged at 1171-1180 feet 
 and 1201-1211 feet. The log is not complete, but shows the lower formations 
 as follows: 
 
 2052-2062 feet shale. 
 2062-2072 feet lime, rock, gas. 
 2072-2073 feet gumbo. 
 2073-2176 feet not logged. 
 2176 feet top of sand. 
 2223 feet total depth. 
 
 The well had either been drilled too deep or "drilled itself" into bottom 
 water by the unrestrained flow of gas. It is likely also that the top water 
 had not been excluded. After the oil production had been completely 
 drowned out, plans were made to repair the well, in order to protect the 
 surrounding territory and to make the well produce again. On account of 
 the double source of water and the large quantity of formation that had 
 been removed during the bljving period, E. E. Winger, then with the Con- 
 servation Commission of Arkansas, advised that the well be abandoned. 
 
 Plate I Busey Well (shown in foreground) Section 31-17-15, the first 
 oil well completed in the El Dorado Field. Well began producing January 
 10, 1921. Photo taken after abandonment of well. 
 
 " 2 - 1 
 
 The well was abandoned during the latter part of April, 1921. under 
 the direction of Mr. Winger and Mr. J. A. Brake, State Oil and Gas In- 
 spector. The abandonment work included cleaning out to bottom, with the 
 hole full of water, placing 90 sacks of thickly-mixed cement on bottom with 
 a dump bailer, and filling the hole full of mud to the surface. The recom- 
 mendation to apply extra pump pressure to the cement in the hole was not 
 carried out, principally on account of the scarcity of suitable equipment at. 
 that time. Plate 1 shows the Busey well and surrounding wells (Septem- 
 ber, 1921). The scarcity of derricks in its immediate vicinity is noticeable. 
 
 Before the end of March, 1921, about twenty oil producers had been 
 completed. The majority of these wells were drilled in a southerly direction 
 from the Busey well. The second and third oil producers were located in 
 Section 6-18-15, the next six in Section 31-17-15; then one in Section 5-18-15. 
 one in Section 32-17-15, one in Section 25-17-16, two in Section 7-18-15, one 
 in Section 30-17-15, four in Section 31-17-15, and one in Section 5-18-15. The 
 development spread rapidly to the south as the productive area was found 
 to extend only about a mile to the north of the discovery well. 
 
 Table 1 shows the number of producing wells, oil production and deliv- 
 eries, stocks, and other data by months from January to October, 1921. The 
 Total oil production of 10,380,000 barrels is estimated and meant to include 
 evaporation losses, seepage and other lease losses, fuel burned in field, oil
 
 EL DORADO. ARK., OIL AND GAS FIELD 
 
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 EL DORADO, ARK.. OIL AND GAS FIELD 11 
 
 used in local refineries, tank car deliveries, pipe-line deliveries and storage 
 oil at the end of October. Some of the factors are admittedly difficult of 
 estimation, but it is reasonably certain that at least 10,000,000 barrels of oil 
 had been removed from the underground reservoir by November 1, 1921. 
 Acreage and Oil Prices: 
 
 Following the completion of the Busey well, which initiated the boom, 
 the area within a radius of several miles from the discovery well, was 
 leased by individuals and corporations. The prices paid for leases ranged 
 from a few dollars to $5,000 per acre, depending primarily on the distance 
 and amount of the nearest production. 
 
 The only outlet for the first production was by tank cars. It was for- 
 tunate that the discovery well was so close (about two miles) to El Dorado, 
 a town of about 5,000 population and served by two railroads. Most of the 
 first oil marketed brought as low as 30 cents per barrel. Some of it is 
 reported to have been sold at that figure, even after The Louisiana Oil & 
 Refining Company opened its 6-inch pipe line on June 24, 1921. This com- 
 pany paid 40 cents per barrel for oil below 34 degrees Baume gravity, and 
 50 cents per barrel for oil above that gravity. On June 17, the Standard Oil 
 Company posted a schedule of 50 cents per barrel for oil less than 33 
 gravity, 60 cents for 33 to 35' gravity and 70 cents per barrel for oil above 
 35 gravity. On September 22 the price went to 80 cents and 90 cents for 
 oils below and above 34 Baume gravity. The maximum limit for water 
 and sediment was 3 per cent. Some of the small purchasers were paying 
 a premium of about 10 cents per barrel. 
 
 Prior to August 15, 1921, considerable oil was sold at figures below the 
 posted prices of the larger purchasers on account of the storage conges- 
 tion. It is reported that a scale of 30, 40 and 45 cents per barrel was in 
 effect simultaneously with the higher schedules and that the smaller pur- 
 chasers often selected only the oil that exceeded 34 gravity and that ran 
 less than 2.5 per cent B. S. and mud. These circumstances appear to have 
 worked some discrimination against the small purchaser after the conges- 
 tion was relieved. By the end of October, 1921, the top price per barrel 
 had reached $1.50, and at present (January. 1922) the posted price is $1.75 
 lor all oil under 34" Baume, and $2.00 per barrel for 34 Baume and above. 
 
 Storage and Marketing Facilities: 
 
 At the end of October, 1921, nearly 4,000,000 barrels of storage had been 
 erected. It was composed of: 
 
 61 55,000 barrel steel tanks 3,355,0:)0 barrels 
 
 9 37,500 barrel steel tanks 337,500 barrels 
 
 Miscellaneous 250,000 barrels 
 
 3,942,500 barrels 
 
 The Louisiana Oil & Refining Company began pumping through its 6- 
 inch line June 24, 1921. The Standard Oil Company of Louisiana started to 
 operate its 8-inch Hue on June 26, 1921, and the Shreveport-El Dorado Pipe 
 Line Company first moved oil through its 8-inch on August 9, 1921. 
 
 Seventeen loading racks with a total capacity of 401 tank cars, or about 
 80,000 barrels, of oil daily were in operation for tank car transportation by 
 the middle of July, 1921. 
 
 There are twelve local refining plants of varying capacities and pur- 
 pose. They have handled only a small proportion of the output of the field 
 up to November, 1921. The following list covers those operating in Jan- 
 uary, 1922: 
 
 Capacity 
 Name Bbls. per Day 
 
 Airdale Oil & Refining Company 500 
 
 Arkansas P. & R. Company 2/JOO 
 
 Abner Davis Ret. Company 500 
 
 El Dorado Oil Ref. Company 2,000 
 
 Orison Ref. Company 5,000 
 
 Jones, R. C 800 
 
 Lion O. & R. Company 5,000 
 
 New-Ark Pet. Corporation 2,500 
 
 Petroleum Products Company 2,000 
 
 Red River Refining Company 1,500 
 
 Shippers Petroleum Company 2,090 
 
 Union Pipe Line & Refining Company 3,000 
 
 26,800
 
 12 EL DORADO. ARK., OIL AND GAS FIELD 
 
 State Conservation Commission: 
 
 The original Arkansas law dealing with the conservation of oil and gas 
 was passed toy the Legislature in 1917. On February 18. 1921, thirty-nine 
 days after the first commercial production of oil in the State, Act No. 144 
 was approved. This Act supplemented the basic law of 1917 and furnished 
 a workable law for the Conservation Commission. The State laws relating 
 to oil and gas are published in a State Report entitled "Minerals in Arkan- 
 sas." 
 
 The Conservation Commission, headed by J. A. Brake, has been handi- 
 capped financially and has, therefore, been unable to extend supervision to 
 all of the important features connected with development. However, it did 
 good work insofar as its funds and personnel permitted. 
 
 The prnicipal regulations which the Commission attempted to enforce 
 are, in substance, as follows: 
 
 (1) Wells that produce gas must be closed in and used for fuel 
 purposes solely. The tendency was to waste enormous 
 quantities of gas in an effort to "blow a well in" to oil pro- 
 duction. 
 
 (2) The casinghead control fittings, usually known as a 
 "Christmas Tree" (see Plate XV) equipment must be 
 heavy enough to insure safety under the pressure obtain- 
 ing and be constructed in a manner to insure control of the 
 well in case of emergency. 
 
 (3) Each well shall be cased with at least two strings of pipe, 
 the first landed and cemented with at least 25 sacks of 
 cement at about 200 feet, and the second landed and ce- 
 mented with at least 60 sacks of cement at a short distance 
 above the oil sand. 
 
 (4) Abandonment of wells shall be accomplished with the use 
 of mud or cement or both in a manner adaptable to the 
 particular case and satisfactory to the Commission. 
 
 At present, there is no money appropriated or tax levied to carry on the 
 conservation work in the State. Because of the treacherous nature of op- 
 erating conditions, supervision by a commission of competent engineers 
 should result in large savings of oil and gas. It would, therefore, be desir- 
 able to provide an adequate annual budget for such a commission, in order 
 to insure a definite and complete program of conservation. This work is of 
 great importance at this time, because of the opportunities to effect con- 
 servation in a new field. Once a field has been improperly drilled, it is 
 usually difficult and expensive to repair the damage. If a new field is dis- 
 covered in Arkansas a trained personnel would be equipped to meet the sit- 
 uation. 
 
 Co-operation by the U. S. Bureau of Mines: 
 
 By the middle of March, 1921, the situation at El Dorado had become a 
 serious problem from the standpoint of conservation. Assistance from the 
 Bureau of Mines was requested by the Conservation Commission, upon the 
 advice of J. H. Mann of the Imperial Oil & Gas Company. Accordingly. 
 E. E. Winger, consulting driller of the Dallas, Texas, office, was detailed 
 to the work. J. B. Kerr, petroleum engineer, was later sent from Dallas to 
 render further assistance. 
 
 The bureau men conferred with operators and did work on wells for 
 the exclusion of water by means of cement, which had to be properly mixed 
 and placed. At times, this involved the use of extra closed-in pressure. In 
 some cases, cement was placed behind the casing to shut off top water, and 
 again bottom water had to be shut off by cement. 
 
 About the middle of April, 1921, Mr. Winger resigned from the Bureau 
 of Mines and joined the forces of the Conservation Commission of Arkansas. 
 He made notable progress in introducing efficient methods of finishing wells 
 and excluding water. J. B. Kerr made drawings illustrating methods and 
 appliances and constructed a contour map, showing the shape of the top 
 of the productive oil sand. 
 
 In August, 1921, the Bureau was able to assign the senior author to 
 the El Dorado field and, with the assistance of J. B. Kerr. sufficient field 
 work was done to warrant the compilation of this report.
 
 EL DORADO, ARK., OIL AND (JAS FIELD 13 
 
 Drilling Methods 
 
 Equipment and Power: 
 
 The use of rotary drilling is rapidly increasing, especially in loose for- 
 mations, and it is now used in practically all loose or soft formations that 
 are deep enough to justify the expense of its installation. Factors working 
 against rotary installation are: 
 
 (1) Usually, a very poor well log is obtained, and many forma- 
 tions capable of production have been passed by without 
 testing. In general, the contents of sands are not so well 
 known in rotary drilled fields as in a cable tool drilled 
 field,, and this results in more wells being drilled into 
 water; 
 
 (2) When the formations are very porous, considerable ex- 
 pense is necessary for extra mud to mud off the porous- 
 mud-absorbing formation and thus allow continuous circu- 
 lation ; 
 
 (3) When the formations are hard and stand up well without 
 mudding, cable tools can be used to advantage, as long 
 strings of casing can be inserted in the open hole; 
 
 (4) When there are frequent changes in formation, from such 
 as hard rock to clay or gumbo, a continual change from 
 rock bits to fish-tail bits is necessary because of the "gum- 
 ming up" of the cone bits in soft, sticky material, and this 
 causes delay. 
 
 The success of cable tools in the El Dorado field is not known, but it 
 is probable that on account of the loosely consolidated formations, it would 
 be more difficult and costly than the rotary method. The wells of the El 
 Dorado field have been drilled to the last water shut-off point, in every case, 
 with rotary tools. The rotary equipment used has varied in character from 
 old style to new style rotaries. Four-inch drill pipe has been used through- 
 out the greater portion of the hole. So far, no installations of high-power 
 twin cylinder steam engine rotaries have been reported. A few wells have 
 been drilled with gas engines and satisfactory results are reported. The 
 comparatively easy drilling at El Dorado makes feasible the use of gas 
 engines of ordinary sizes. The boiler installation can thereby be greatly 
 reduced and of sufficient size to meet the needs of operating the pumps and 
 forge. The gas engines are equipped with an electric magneto, an electric 
 Wyco coil type or compressioihot point system of ignition. The old system 
 of hot tube ignition is not used in this work, because of its unreliability 
 and the danger of an open flame in a gas-producing area. It is necessary 
 to use an ignition system that can be correctly adjusted by the men 
 available, because of the excessive strains in the engine and loss of power 
 which results from improper timing. 
 
 Electric power for drilling has not been used at El Dorado, Arkansas. 
 Although electric drilling has proven efficient and economical in other fields, 
 its introduction in Southern Arkansas has been retarded by the absence of 
 available power (unless private generating plants are constructed) and by 
 the lack of familiarity of the local operators with the system. It is true 
 That more energy can be developed with oil or gas by means of internal 
 combustion engines than by generating steam with the same fuel. How- 
 ever, economy of power does not always dictate the practice in oil and gas 
 fields, where gas is cheap and not marketable. 
 
 The generation of electricity by means of internal combustion engines 
 has proven economical in many cases for drilling and general use on oil 
 properties. This is especially true when cheap gas is not available and oil 
 is used as the explosive fuel. Under certain conditions, it is more econom- 
 ical to generate electricity with steam turbines and transport it by power 
 lines than to use the steam direct through long uninsulated pipe lines. 
 There are many factors that determine the most practicable power to use 
 for drilling. Mechanically, steam is well adapted to the work and because 
 of the abundance of gas, with a limited market, it was used extensively in 
 the El Dorado field. 
 
 In the fields where it has been tried, the electric motor for dri'ling has 
 proven satisfactory from a mechanical standpoint for both standard and 
 rotary work and very often reduces the cost of operations. A 75-horse-
 
 14 EL DORADO. ARK., OIL AND GAS FIELD 
 
 power motor is usually installed for drilling and a 40-horse-power motor To. 
 the mud-circulating pumps. The principal advantages over steam operation 
 are the omission of boiler installations and repairs and almost complete 
 elimination of water requirements. 
 
 Casing Programs: 
 
 Wells in this field are cased with at least two strings of pipe, the first 
 being l2 l / 2 -inch or 10-inch conductor pipe which is cemented at about 200 
 feet and the other a water string of usually ti-inch 8-thread pipe. In some- 
 wells, 8-inch pipe has been used as a second string, but probably in no case 
 has it been used as the final water string. The general practice has been 
 to check the hole and casing measurement with a steel tape. Some serious 
 errors in measurements, however, are reported to have resulted in casing 
 off oil or drilling into water. It is practically impossible to know the exact 
 depth of the hole by adding the figures for lengths of joints of casing. 
 
 The smaller pipe used in El Dorado usually has 8 threads per inch. 
 The larger sizes having 10 threads per inch are 12%-inch 40 pounds; 10- 
 inch 32 and 35 pounds; S^t-inch 32 pounds. Sizes of casing having 8 threads 
 per inch are 8-inch 29.2 pounds and 6-inch 19.5 pounds. The liners are dif- 
 ferent weights of 4-inch to 4 1 /-inch pipe. 
 
 There have been no cases of collapsed casing reported to the writers 
 thus far, because El Dorado operators in most cases used good weights of 
 casing for the depths. Comparatively shallow depths to the shut-off point 
 and small sizes of casing used have also assisted in preventing collapse. 
 In Table No. 2 (a), the collapsing depths of various casings are shown in 
 connection with the other data. Table No. 3 (b) shows the amounts of 
 cement required for different sizes of casings and holes. Both of these 
 tables were prepared at the Denver, Colorado, office of the U. S. Bureau of 
 Mines, under the direction of F. B. Tough. 
 
 In selecting casing for a water string, attention should be given to its 
 weight in order to avoid collapse by outside water or mud pressure. How 
 ever, collapsed casing cannot be prevented when formations shift. The best 
 practice is to choose a string of casing that will stand the fluid pressure at 
 the prescribed depth with a safety factor of two. If a given size and weight 
 of casing is supposed to collapse by an external pressure due to 3,000 feet 
 of effective water column (1,302 pounds per square inch), that casing should 
 not be used to a depth greater than about 1,500 feet below the natural water 
 level outside the casing unless enough cement is used to protect a con- 
 siderable length of the lower portion of the casing. When rotary drilling is 
 employed, the gravity of the mud and the full column outside the pipe to 
 the surface, must be considered. For example, if the rotary mud back of 
 the casing has an average specific gravity of 1.25 (25 per cent heavier than 
 water) or 5/4 the weight of water, a given string of casing for safety 
 should have an effective column of mud, on the outside of the pipe, of only 
 4/5 of the safe depth for clear water as recorded in Table II. Another way 
 to arrive at the safe depth for casing in mud is to divide the safe water 
 depth by 1.25. or whatever happens to be the specific gravity of the mud. 
 If it could be assumed that the fluid standing outside of the casing would 
 remain undisturbed, a factor of safety 1.5 or 1.4 might be considered. Earth 
 tremors and shifting of formation may have considerable water-hammer 
 effect, regardless of whether the walls actually squeeze the casing. 
 
 It is usually found economical for deep wells, to make up suitable com- 
 bination strings with the heaviest pipe on the bottom and the lengths oi 
 the lighter weights proportioned according to their safe depths. In many 
 oil fields, two different weights of pipe are often used, but a combination of 
 three is less common. As far as is known by the writers, no combination 
 strings have been used at El Dorado. 
 Testing Formations: 
 
 In at least the first work of developing underground deposit ; of oil and 
 gas in any area, drilling methods should be modified in such manner as to 
 give the most accurate knowledge of formations and their fluid content. 
 There are many examples of wildcat wells condemning territory by passing 
 through commercial deposits without testing them and, in some case?, 
 without suspecting their presence. There are also many instances where 
 high-pressure oil and gas have been found without any particular care being 
 taken, but where the preseiice or capacity of upper deposits remain un- 
 known, and the exact nature of -the producing horizon was not learned. Oil
 
 EL DORADO, ARK., OIL AND GAS FIELD 
 
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 16 EL DORADO. ARK., OIL AND OAS FIELD 
 
 deposits that are now commercially productive or that may become so 
 within a reasonable period, should be protected from infiltrating water and 
 from dissipation into other strata. Without a comprehensive knowledge of 
 all of the formations penetrated, it is impossible to know whether and how 
 to protect strata for future use. 
 
 In some fields, cable tool drilling is generally the best adapted to the 
 accurate determination of underground conditions. Unfortunately, this 
 method cannot be used in many fields, because of the soft and caving nature 
 of the formations. Satisfactory results can be obtained with the rotary sys- 
 tem if sufficient care is exercised. In order to obtain adequate knowledge 
 with rotary, samples should be taken from the ditch at least every ten feet 
 of hole made. The speed of the upward current of mud should be figured and 
 the samples checked back, through the time interval, against the feel of 
 the tools and action of the pumps. As the driller relies mainly on the feel, 
 to detect a change of formations, cuttings should be studied with relation 
 to changes noted iby the feel. Samples of porous material should be care- 
 fully examined to determine the fluid content. When practicable, the core 
 barrel should be used repeatedly when nearing the productive horizons. 
 The core is a correct sample of the formation and will usually disclose the 
 presence of any oil in the stratum. The future of accurate information 
 obtained from rotary-drilled wells is dependent to a large extent on a prac- 
 ticable method of sampling formations and, at present, the core barrel 
 seems to have the most promise. 
 
 It is advisable to test a sample from the ditch with chloroform, ether 
 or carbon tetrachloride, in order to indicate the presence or absence of oil. 
 In making this test, the sample should be thoroughly shaken with the sol- 
 vent and allowed to settle for some time and the liquid then run through 
 white filter paper. If petroleum is present in appreciable quantities, a dark 
 ring will appear on the filter paper. 
 
 In general, ditch samples are obtained in two ways. Some drillers thin 
 The mud, while others thicken it and increase the speed of circulation. Both 
 methods possess merit and are usable for the same general purpose, though 
 the principles are somewhat different. Thinning the mud lightens the 
 weight of the column of liquid in the hole and decreases the pressure oppo- 
 site the sand, so that any oil or gas can come into the hole more easily. 
 
 Gas is somewhat soluble in water. Methane, the largest constituent of 
 natural gas, is 3.9 per cent (*) soluble in water at ordinary temperature 
 and pressure. It is probably much more soluble at the increased pressures 
 obtaining underground on account of the compressibility of gas and the non- 
 compressibility of water. The solubility of gas in water assists it in trav 
 eling from the formation to the hole, because when a substance is dissolved 
 in a liquid, it tends to diffuse equally to all parts of the liquid. Hence, solu- 
 bility and diffusion help to explain why a gas is able "to show" when the 
 fluid pressure exceeds the rock pressure. Such a condition may exist when 
 the sand is not taking water and a condition of stability exists. When the 
 gas enters the hole, it rises through the water on account of the difference 
 in weight and the high fluidity of the water. Thin mud then gives the gas 
 and oil a better opportunity to enter the hole. There are, however, many- 
 deposits that will not "show" against a hole lull of muddy water or even 
 clear water. If light gravity oil shows under such conditions, it is manifest 
 that there is considerable pressure to force it into the hole. 
 
 When mud is thickened and the speed of circulation increased, larger 
 particles of formation are buoyed up and discharged at the surface. In 
 this way, particles as large as peas may be obtained in the samples. If the 
 thick mud does not wash through such pieces, they will, in some cases, 
 indicate the presence or absence of oil by solvent test or bv more inser- 
 tion. This method oftentimes gives an indication of the presence of gas as 
 well, for the gas will "show on the ditch" in the form of babbles which rise 
 to the surface of the mud and burst. 
 
 When the rock-pressure is not sufficient to expel the mud and water 
 from the hole, the only means of estimating the productivity of the sand is 
 to lower or remove the drilling fluid from the hole by bailing. Even that 
 is sometimes not sufficient to prove commercial production, and swabbins 
 
 * Hill, H. H. Supt., i'. S. Bureau of Mines Experiment Station. Bartlcsrillc. 
 Oklahoma personal rotniiniitication.
 
 EL DORADO, ARK., OIL AND GAS FIELD 
 
 17 
 
 or rewashing is resorted to in order to bring in the oil or gas. It is, of 
 course, necessary to fully protect the walls of the hole from caving while 
 making a bailing test. The usual procedure in such a test is to remove the 
 drill stem and insert the pipe with a packer and with a suitable amount of 
 perforation so placed as to be opposite the formation to be tested when the 
 pipe is set. 
 
 If complete data of other wells are collected and compiled by the en- 
 gineer for the purpose of selecting depths to test, it becomes relatively easy 
 to test at those depths. For instance, if it is desired to make a test of the 
 formation between 1,160 and 1,200 feet, the drill hole can be stopped at 
 about 1,150 feet in a tapered hole and the casing set without perforations. 
 A small hole can then be drilled ahead to the desired depth and the mud 
 bailed from the casing without much danger of disturbing the mud and 
 formations on the outside of the casing. When the oil-bearing formation 
 has already been passed through, which is often the case, the pipe is usually 
 set on bottom and some sort of suitable packer attached above the per- 
 forated portion in order to retain the mud. The so-called mother-hubbard 
 packer of the inverted umbrella type and made of canvas, burlap, rope or 
 leather, has been used with success and economy for such work. In many 
 cases, such a packer does not effectively exclude top water, and in that 
 event the test is of little or no value. Enough packing material should be 
 used to insure against buckling past and down the casing. The telescoping 
 packers, carying rubber or hemp, also are used. For their successful use, 
 the bore-hole should be circular and smooth and of about the diameter ex- 
 pected. A hard shell to set this type of packer in is also desirable. 
 
 If a temporaray shut-off can be effected, the mud should be slowly bailed 
 from the casing, after providing the proper control fittings. Obviously, 
 these appliances are likely to be of little use for high-pressure unless means 
 are provided for retaining the pressure on the outside of the casing. It is 
 desirable to braden-head the casing to the conductor pipe or other string of 
 casing, else there will be danger of a well blowing wild outside of the 
 casing. 
 
 Plate II shows a crew in the El Dorado field bailing down the mud in 
 a well that is expected to come in any minute. Gas has already appeared 
 in this well. The "Christmas Tree' is fitted with a valve below and one 
 above the lead lines. In case the well should blow in with high gas pres- 
 sure, both valves can be closed on the sand line. The only waste would be 
 a spray around the line, but the main flow of oil would be diverted through 
 the lead lines shown in the foreground. 
 
 Plate II Bailing Down to Bring in Well. Connections Made for Flowing 
 
 Well.
 
 18 EL DORADO, ARK., OIL AND GAS FIELD 
 
 The practice at El Dorado of cementing a conductor string at about 
 200 feet, is an excellent one. If this is done, any formation can be safetly 
 tested by braden-heading or packing off between the testing string and the 
 conductor. It may be argued that the upper showings at El Dorado are 
 known to be of low pressure and of little commercial importance, because 
 a few tests have indicated that condition. The main oil zone in the field 
 is apparently not uniform and the upper strata in general are also irregular 
 in occurrence. It is quite possible, then, that upper horizons may occur 
 "which are commercially productive in certain areas and that the few tests 
 have not been conclusive. 
 
 The mad scramble with which operators conducted their rotary drilling, 
 jn order to reach the known productive zone has resulted in meager infor- 
 mation concerning the nature of the upper deposits. A number of wells 
 .have logged showings of oil or gas. For instance, a strong showing of gas 
 and oil in twenty feet of good sand was reported at 1,800 feet depth in a 
 well on Section 8-18-15. This deposit was mudded off in the usual way. If 
 the correct gravity of the upper oil could be obtained, it would aid in an 
 estimation of its value. It is obvious that if a bed of tar or very heavy oil 
 is penetrated, it will probably be noted on the ditch, for the reason that it 
 is not readily driven back into the strata by the mud and water and sticks 
 together better than lighter oil. When light oil shows in the presence of 
 a full column of mud, there is apt to be considerable pressure behind it and 
 it is worth testing to determine its productivity. 
 
 If there are upper oil and gas deposits of present or near-future com- 
 mercial value, that fact should be known before the wells are finished, and 
 adequate provision made to protect them. Before the wells in a certain 
 district are abandoned, enough tests should be made to determine the pos- 
 sibility of utilizing the upper sands. It is obvious that if upper production 
 is obtained, it must be protected from any top water lying below about 200 
 feet. So far, no special attention has been given to the protection of any 
 upper oil sands from top water, and on this account it may be impossible 
 later to get a fair test of the upper sands until the upper water is excluded. 
 
 In this connection it should be mentioned that the mud-fluid column 
 cannot always be relied upon to protect upper oil sands against water in- 
 filtration, especially with the common method of circulation with no extra 
 closed-in pump pressure. In older fields, gas is often found issuing from 
 behind casings landed with rotary. As time elapses, even thick rotary mud 
 may gradually settle out and allow gas to blow out and water to travel from 
 its native formation. The results of such action are illustrated in A and B 
 of Plate III. Thus a valuable deposit of oil may be somewhat flooded with 
 water before production is attempted. The time to protect oil deposits 
 from water and from dissipation into low-pressure porous strata is during 
 the drilling of the wells. 
 
 This discussion is not a prediction that extensive valuable upper de- 
 posits exist. The possibility exists and a more thorough inventory should 
 be made by conducting tests whenever possible. When drilling is done by 
 contractors, a qualified representative of the company should keep almost 
 constant watch of the samples and should be able, under the contract, to 
 make a complete test at any point desired. 
 
 Completing Wells: 
 
 In order to avoid serious mistakes, when drilling in a territory lacking 
 easily recognizable marker formations, considerable care must 'be exercised 
 in determining the final point for excluding top water and in selecting the 
 final depth to drill the well. 
 
 It is, of course, necessary to shut off low enough to get below all top 
 water and to stay above the oil sand. There is considerable leeway for 
 the shut-off point at El Dorado, as a number of tests have indicated that 
 there is no water nearer than about 100 feet above the top of the oil sand. 
 
 In drilling into the oil formation, it is important to use great care (1) 
 to avoid drilling to a point within short range of edge water, (2) to avoid 
 drilling into bottom water, and (3) to avoid permanently mudding off or 
 seriously injuring low-pressure oil and gas. 
 
 If it is known that in certain locations, edge water lies under the oil 
 and along the bottom of the oil sand, the hole should merely penetrate the 
 top of the sand or extend into the sand only a small percentage of its thick-
 
 EL DORADO. ARK., OIL AND GAS FIELD 19 
 
 ness. In this way considerable oil will be allowed to drain laterally, before 
 the water can overcome friction and gravity and crowd the oil back. This 
 means of conservation fails if the production is not controlled to a certain 
 degree. If too great an output of fluid is allowed, the water will soon find 
 its way into the well, on account of its low viscosity (high fluidity) and will 
 "cone" the oil back, as shown in Plate IV. Quite a number of El Dorado 
 wells have gone to water prematurely on account of drilling too deep into 
 the sand or by not sufficiently restraining production, thereby causing the 
 well to drill itself deeper or causing the water from below to be sucked up 
 through the intervening sand. 
 
 The term "bottom water" is here used to mean water that underlies 
 the oil sand and is separated from it by a more or less impervious parting. 
 Plate IV shows the apparent relationship of the oil and water. Some of the 
 wells in the southern portion of the field have no doubt drilled into bottom 
 water on account of finding no cap above the oil sand. The cap at the bot- 
 tom of the sand was sometimes mistaken for the cap above the oil sand 
 and the well was drilled into bottom water. Sufficient care was not used 
 in determining the character of the formation, the presence of oil was noted 
 too late and its exact source was misinterpreted. Other wells have been 
 drilled into bottom water through lack of proper direction. Much of that 
 could have been avoided by the application of ordinary engineering meth- 
 ods, which allowed conclusions to be reached from a study based largely 
 on the data of neighboring wells. Full consideration should be given to the 
 elevation of the wells, the pitch of formation in different directions as 
 shown by logs (see cross sections of Plates V and VI) and the known in- 
 tervals between marker formations, the top of sand and bottom water. 
 Failure to consider these factors has cost the operators dearly. A study 
 of the well logs of these two cross-sections shows that in most cases the 
 oil sand is the principal marker. 
 
 Considerable harm is likely to be done by allowing excessive mud and 
 water to penetrate low-pressure oil and gas strata. When the formation is 
 not very porous, it may be better to plaster it up with thick mud and avoid 
 mudding a great distance. When the formation is quite porous, it would 
 appear better to drill in with water rather than mud. The water would 
 be more readily expelled into the hole again and would act as a less effec- 
 tive choke. The wells of El Dorado have to date had fairly high pressure 
 with which to free themselves of rotary mud. Because of declining gas pres- 
 sure, however, future Wells will not clean themselves so readily. In other 
 fields, wells have been drilled with rotary and called dry, after which some 
 of the formations penetrated have been proven highly productive. There 
 may possibly have been such cases in the El Dorado field also. 
 
 Certain operators report that there is little opportunity to determine 
 the top of the oil sand by taking core barrel samples of the formations 
 when approaching the oil sand, on account of the incoherence of the porous 
 material. The writers believe, however, that too little attention has been 
 given to core-barreling in El Dorado, because such work has been very suc- 
 cessful in other fields where conditions are somewhat similar. 
 
 A few of the wells have been finished with cable tools and that method 
 is more satisfactory than the rotary tools, for the following reasons: (1) in 
 order to pump the well, it must be partially equipped with standard cable 
 tool equipment and, therefore, the work of changing the rig to suit cable 
 tools is not lost; (2) the drilling may be done without mud and usually 
 with much less fluid in the hole; (3) running the bailer to clean out the 
 drill cuttings gives accurate formation samples every few feet, and a sam- 
 ple can be obtained at any depth desired with little delay. In some fields 
 with loose caving oil sand, only a small amount of open hole can be drilled 
 in cable tool work, ahead of the pipe, but at El Dorado it is not advisable 
 to drill more than a few feet into the oil sand, so that the liner can be 
 placed with cable tool equipment. 
 
 Mr. Winger, who initiated the finishing of wells with cable tools at 
 El Dorado, has communicated the following information on the rotary 
 method of completing wells: 
 
 "In drilling with a rotary it is frequently impossible to determine the 
 exact nature of the formation being drilled, for the reason that it takes 
 some thirty minutes to get cuttings from the bottom of a 2,000-foot hole and
 
 20 EL DORADO. ARK., OIL AND GAS FIELD 
 
 there is also good opportunity for samples being mixtures of different forma- 
 tions. I know of an instance in this field, where the drillers thought they 
 were' in shale and decided to test it out and see if it was bearing any water. 
 They ran the bailer four or five times and the well came in, one of the best 
 in the field. No liner had been set or other necessary preparations made. 
 
 "Another instance: A certain company in this field drilled an offset to 
 a well, the sand depth of which was known. This depth was reached, but 
 there was absolutely no showing not a rainbow, gas bubble, or cutting that 
 indicated anything. But the neighboring well had been drilled too deep 
 and it was necessary to plug back to shut off salt water before making a 
 well of it. So this company stopped there where the "pay" should be and 
 after bailing about twelve hours brought in their well. This test would 
 not have been made at that point had they not known the exact depth to 
 the "pay" in their neighbor's well. In cable tool drilling, the cuttings are 
 brought out of the bottom of the hole each time with the bailer and there 
 is not so much guess work. 
 
 "If the rig is standardized, the expensive rotary equipment does not 
 have to remain idle ten days waiting for the cement to set, but is released 
 to another location. A number of big wells in this field, brought in by 
 rotaries, have bridged and sanded up soon after the machinery was moved 
 off. The owners lost enough production, waiting to get machinery back on 
 the well to clean out, to pay for standardizing. It takes several days to 
 rig up a rotary and get it back on the job, if one is available, whereas if 
 the well is standardized the tools and sand pump can be run and production 
 resumed in a few hours." 
 
 The operators of El Dorado who have tried completing wells with cable 
 tools, have found it highly satisfactory and express their intention to con- 
 tinue the practice. 
 
 When finishing wells with cable tools in high-pressure territory, it is 
 sometimes necessary to use care in removing the tools from the hole, lest 
 the well blow in. The "lubricator" shown in Figure 1, when properly used, 
 will prevent blowouts. In at least one instance at El Dorado it was used 
 with success. Usually a short string of drilling tools can be used for finish- 
 ing, as speed is not so necessary at this place in the work. The drilling is 
 done through the control head (a) and the master gate (k). The assembled 
 lubricator parts (a), (b) and (c) are hung above the beam with the drill- 
 ing line passing through them. When the drilling is finished, the lubricator 
 is lowered and screwed into the lower control head (a). The upper control 
 head (a) and oil saver (b) are then closed somewhat on the line and the 
 tools are pulled up to the position shown. The master gate and lower con- 
 trol head can then be closed, the lubricator removed and preparations made 
 for bringing in production. 
 
 Although careful rotary drilling gives good results in many instances, 
 it appears certain that the field would be making less bottom water today 
 if all of the wells had been finished with cable tools in the hands of compe- 
 tent drillers. 
 
 There is probably not a well in the El Dorado field that has used a full 
 oil string for producing. Perforated liners or screen pipe or a combination 
 of both are generally used. The loose sand problem is difficult of solution 
 and greatly retards production. It will be discussed under "Production 
 methods." 
 
 Labor Conditions: 
 
 The nation-wide rush for oil, with high prices for oil, which was 
 initiated by the demands of the World War, resulted in much wildcatting 
 and the opening of many new fields. In order to handle the vast amount 
 of work, it was necessary that men with little oil field experience be en- 
 trusted with important phases of development and production. A compe- 
 tent oil man cannot be developed in a few months or even years, and hence 
 tnere has been much mismanagement and poor workmanship. The El 
 Dorado field has suffered considerably from this condition, which probably 
 cannot be righted for some time. 
 
 The following example of poor handling was furnished by a driller fami- 
 liar with the work on the particular well: A well was drilled with rotary 
 tools to the depth estimated from the logs of neighboring wells, as sufficient 
 to encounter the oil sand. The mud was thinned considerably and a show 
 of gas appeared. Without thickening the muddy water and without keep-
 
 EL DORADO, ARK., OIL AND GAS FIELD 
 
 21 
 
 LEGEND 
 
 a Control Head 
 b Oil Saver 
 c Two Joints 6" Pipe 
 d Valve 5terr, 
 
 Flow Line 
 
 Bull Pluc, 
 
 Clamps On e"PTpe 
 
 Clamps On 10" -Pioe 
 Tools 
 
 Master Gate 
 10' Pipe 
 Valve Wnsncb 
 
 FIGURE! 
 
 Fig. 1. Cable Tool Lubricator for High Pressure Walls.
 
 22 EL DORADO. ARK., OIL AND GAS FIELD 
 
 ing the hole full of fluid, the drill stem was withdrawn from the hole as 
 rapidly as possible. The driller stated that this was done in order to get 
 the casing in as soon as possible. The removal of the drill stem lowered 
 the fluid in the hole and the well blew out before the drill stem was with- 
 drawn. About 1,300 feet of drill pipe was dropped to the bottom. The wild 
 flow either drilled the well into bottom water or sucked up edge water and 
 the production turned largely to water. The fluid ran into earthen sumps 
 and much of the oil produced was lost in spray, evaporation and seepage. 
 It becomes difficult to repair such a well on account of the large cavities 
 formed by blowing out sand and on account of the damage done to thin im- 
 pervious partings that may exist 'between the oil and water. This well was 
 ruined by improper handling and in addition to the loss of the hole and re- 
 sultant expense it has, no doubt, done great damage to the surrounding ter- 
 ritory. 
 
 Drilling Costs: 
 
 The majority of the wells at El Dorado have been drilled by con- 
 tractors. On account of easy drilling, the wells are completed at approx- 
 imately 2,200 feet in about thirty days. Some of the first contracts called 
 for a completion of the well, ready to flow, for $25,000. These were known 
 as "turn-key" jobs. Since labor and material have become cheaper, and. 
 more competition has entered into contracting, the price has been reduced 
 to about $12,000 or about $5.50 per foot. One operating company reports 
 considerable saving by drilling their own wells. Using $5.50 as the con- 
 tract basis, it is stated that a saving of from $0.59 to $3.90 per foot has been 
 accomplished. These figures represent a total saving range of $1,300 and 
 $8,490 per well, respectively. The average reported saving was $2.81 per 
 foot. The cost for 200 feet of 10-inch and 2,100 feet of 6-inch 8-thread line 
 pipe is at present (November. 1921) about $3,000. The contract price for 
 a 112-foot rotary derrick is $800. The cost of derrick and combination rig 
 (rotary timbering and standard rig irons and wheels) is about $1,500. The 
 cost of casing and rotary derrick is included in the $12,000 for a "turn-key" 
 job. 
 
 The prevailing wages for rotary crews in October, 1921, was $10 per 
 12-hour period for drillers and $5 each for the remainder of the well crew. 
 
 Water Conditions 
 
 Amount of Water Produced: 
 
 The amount of water produced in the Ed Dorado field is difficult to 
 approximate, because of the failure of operators to gauge the water produc- 
 tion as a whole or from individual wells. A large proportion of the water 
 produced is bled from the separators as free water. As the water comes 
 from the bleeder lines through "cracked" valves, it is under considerable 
 pressure and is, therefore, in the form of small high-velocity streams and 
 spray, rendering estimation very uncertain. Much water escapes by run- 
 ning into streams and sinking into the ground. 
 
 A large proportion of the water from numerous wells passes into the 
 first storage tanks as emulsions. After this emulsion is broken up by spe- 
 cial treatment, the amount of water present is not usually measured. 
 
 Estimates of total water production by those familiar with field condi- 
 tions, range from 25 to 50 per cent of the total fluid raised. Operators who 
 are more familiar with conditions in the north end of the field are apt to 
 under-estimate the water production, while those of mostly south-end ex- 
 perience are likely to over-estimate it. 
 
 It is believed by the writers that at least one-third of the gross produc- 
 tion in October, 1921, was water. At any rate, the amount of water being 
 recovered with the oil is enough to cause serious alarm concerning the life 
 of the field. 
 Harmful Effects of Water: 
 
 The very rapid decline of production in this field is no doubt caused by 
 water, more than by any other factor. All operators of wide experience with 
 production of this character realize the harmful effects of water under cer- 
 tain conditions, and so much has been written on the subject that only gen- 
 eral references are given to some publications of the U. S. Bureau of 
 Mines.*
 
 EL DORADO, ARK.. OIL AND GAS FIELD 23. 
 
 The physical properties of oil and water are widely different. Water 
 is considerably heavier than El Dorado oil, is more fluid (less viscous) at 
 ordinary temperatures, and has greater surface tension. Each of these 
 characteristics of water gives it an advantage over oil when the two liquids 
 are competing for passage through the reservoir rocks toward the wells. 
 Water is also very effective in "killing" gas action, especially when the 
 sediments are of close texture. 
 
 The weight of water standing in a well exerts a hack-pressure on the 
 oil in the formations and tends to hold it there. When oil once reaches 
 the well there is, of course, nothing to prevent it from rising to the top of 
 the fluid column, it being lighter than water. 
 
 Viscosities of liquids are measured by means of a viscosimeter, and 
 this instrument demonstrates that water is more fluid than oil. For the 
 benefit of the field man, a brief description is given. It is essentially a tall 
 cylindrical vessel with a small standard spout opening in the side at the 
 bottom. The viscosity of liquids are compared by the time it takes to 
 empty the vessel through the orifice. It is thus shown that water will move 
 through small openings much more freely than will oil. 
 
 If water and oil are present in a stratum penetrated by a well, although 
 the water will occupy the bottom portion, drilling too deep or removing 
 the fluid too rapidly, will allow the water to rush into the well and crowd at 
 least some of the oil back. Gas pressure is, in general, the principal force 
 that carries oil toward a well, the force of gravity being of only minor im- 
 portance, especially in strata of low inclination and small thickness. Ex- 
 cessive water will reduce or "drown out" all but high-pressure gas with dis- 
 astrous effects on production. 
 
 Water has greater surface tension and is attracted more strongly by 
 the formations than is oil. The force, known as capillary attraction will 
 draw water upward in much the same way that a wick supplies oil to a 
 flame. The water tends to "grip" the formation particles and thereby re- 
 tards the movement of oil and gas. That force is strongest in fine-grained 
 material or in minute crevices and the greatest retardation of movement by 
 water can, therefore, prevail in such material. As an illustration, consider 
 two sands that are each composed of spherical grains. The grains of sand 
 A have a diameter of .005 inch, while those of sand B measure .050 inch, or 
 ten times greater. Each sand has the same percentage porosity and will 
 hold the same amount of fluid. Movement can occur more easily in B than 
 in A, because there is less frictional resistance and less capillarity on 
 account of the larger space between the .grains. 
 
 Source of Water: 
 
 There is little doubt that over 90 per cent of the water produced at 
 El Dorado is a combination of bottom water, which underlies the oil-bearing 
 strata and appears to be uniformly separated from it by a cap rock, and" 
 edge water which is present in the down-dip and lower portion of the oil- 
 bearing strata. 
 
 It is not unlikely that some faulty shut-offs are letting in top water, but 
 from the data at hand this source appears insignificant. The minimum re- 
 quirements of the Conservation Commission for water strings, are twenty- 
 five sacks of cement to set thirty-six hours for 170 feet of shallow string 
 and sixty sacks of cement to set ten days in the case of the final string, 
 which is usually 6-inch 19%-pounds pipe. A test of water shut-off is re- 
 quired on the main water string. If the test is not satisfactory, the condi- 
 tion must be remedied before drilling into the oil. The operator should be 
 more anxious to exclude the water than any one else, but as he cannot always 
 be present at such tests, the responsibility may be left with the foreman, 
 driller or contractor, who is often careless about such work. It would be 
 desirable for a Conservation Commission officer to witness all tests for 
 
 ^Bulletin No. 134, The Use of Mud-Laden Fluid in Oil and Gas Wells, by 
 J. O. Lewis and W. F. McMurray, 1916. 
 
 ^Bulletin No. 163, Methods of Shutting Off Water in Oil and Gas Wells, by 
 F. B. Tough, 1918. 
 
 *Bulletin No. 195, Underground Conditions in Oil Fields, by A. W. Am- 
 brose, 1921.
 
 24 EL DORADO, ARK., OIL AND GAS FIELD 
 
 water shut-offs. The results of each test could then be reported and an 
 adequate record kept by both the operator and the Commission, which would 
 be of value in future work. 
 
 A number of circumstances may arise that cause water shut-offs to leak. 
 They will be mentioned as of possible value in determining upon the source 
 of water in this field: 
 
 (1) Running casing in hole may loosen threads and cause leaks. This 
 is not so apt to happen with mud back of the casing as with water. Often- 
 times, casing is not screwed up tightly and by putting on tongs and screw- 
 ing up, the water may be shut out. Source of leak can be determined by 
 running casing tester or by setting a packer on tubing. Before drilling out 
 cement for test of shut-off, the tightness of the casing itself should be ascer- 
 tained by bailing out the mud or water and letting the well stand undis- 
 turbed for about five hours. If nothing collects in the bottom, other than 
 that reasonably expected as drain-back, the casing may be considered tight. 
 If a large quantity of cement has been used and a large proportion of it 
 sets inside the casing, it may become necessary to test the lower portion 
 of the casing after the cement is drilled out. 
 
 (2) Casing may be imperfect in places or may develop breaks while 
 running in. If second-hand pipe is used in high-pressure territory, it is well 
 to test each joint with hydraulic pressure before using. In the Monroe, 
 Louisiana, gas field some of the operators test their casing and fittings with 
 a special apparatus. A description and photograph of such apparatus can 
 be found in Bulletin No. 9 (pp. 55. 56) of the State of Louisiana, Depart- 
 ment of Conservation, a co-operative report written by H. W. Bell and R. A. 
 Cattell of the Bureau of Mines. In testing one string of 6-inch, 19%-pound 
 pipe, at the factory, twenty out of the sixty joints leaked, and one joint 
 split about fifteen inches on one end under an internal pressure of less than 
 1,200 pounds per square inch. 
 
 (3) After determining that the casing does not leak, the cement should 
 be drilled out and the well drilled to the formation in place. For safety, 
 drilling should be stopped when about one foot into the formation. If a new 
 water or oil and gas stratum is encountered at the shoe, it will be impos- 
 sible to test the effectiveness of the shut-off. 
 
 (4) After drilling out cement and bailing down for test, drilling mud 
 and water may rise to a high level, due to being returned from porous for- 
 mations adjacent to the shoe. Indeed, it may require a number of tests to 
 show that such inflow is decreasing and is exhaustible and that the cement- 
 ing operation was a success. 
 
 (5) If too much hole is made for the test and new water is encoun- 
 tered below, that fact may not be recognized until after considerable work 
 is done. The shoe may be in the middle of a water-bearing formation, a 
 very short distance above it, or a considerable distance above it. In the 
 first case, it may be impossible to demonstrate the source. In rotary wells 
 it should, in all cases, be noted whether mud is coming in, and in every 
 case whether known upper deposits are supplying oil or gas around the 
 shoes. If a good dye is placed behind the water string and shows up at 
 the shoe, the test indicates the water string is leaking, but if it does not 
 appear, nothing is proved. In the second case, it may not be possible to set 
 a cement or other plug to exclude the water from below and, at the same 
 time, leave a little open space below the shoe. If the dye test fails, the 
 source might be proven, as has been done elsewhere, by plugging the forma- 
 tion with cement and up to about two feet into the shoe; then perforating 
 the water string a few feet above the shoe, until formation comes in. The 
 kind and amount of fluid that enters will probably indicate the source of 
 water. It is a dangerous thing, however, to punch holes in a water string 
 and this should be done only as a last resort. In the third case, the 
 source could be demonstrated by placing a cement bridge just below the 
 shoe or possibly by setting a packer in formation just below the shoe, and 
 making a bailing test. 
 
 In some fields, where cable tools are used samples of each water en- 
 countered, or at least a composite sample of all top water, are obtained 
 and analyzed. In this way the source of water is usually easily deter- 
 minable by comparison with the analysis of water in question, as the 
 chemical characteristics of the mineral content of oil-field water usually 
 change considerably with depth. A comparison of fluid levels and of
 
 EL DORADO, ARK., OIL AND GAS FIELD 25 
 
 amounts of the known and unknown water is often sufficient evidence of 
 the source. With rotary drilling, these methods are impossible, except in 
 rare cases'. 
 
 (6) Besides making sure that the cement has been drilled through 
 for a test, no shut-off should be passed unless the hole can be kept cleaned 
 out to bottom. Heaving formation may bridge and hold back water. 
 
 (7) In drilling out a considerable distance below the shoe of a water 
 string, oil-bearing formations may be penetrated or re-exposed and the test 
 of shut-off thereby rendered more difficult or inconclusive, due to the oil 
 or gas coming into the hole. In such cases, it is usually not possible to 
 plug off the oil or gas without also sealing the shoe of the water string. 
 The only recourse then is to make a production test in an effort to de- 
 termine the condition of the shut-off, either by producing from present 
 depth or after deepening for more production. The former method, that 
 is, before deepeneing, is more reliable because deeper drilling may en- 
 counter lower water. Obv-iously, the production test is not conclusive 
 unless the well settles down to a clean production and it should, therp- 
 fore, be avoided, except as a last resort. 
 
 The liability of error in measuring the depth of the shoe is believed 
 by some to be sufficient reason for drilling out an excessive amount below 
 the shoe. However, there is no call for such procedure if broken cement 
 and formation are brought to the surface. 
 
 In general, the determination of the source of water in a well or 
 group of wells, can be indicated by the use of the following: 
 
 (1) Formation, production and casing records of wells. 
 
 (2) Graphic means to visualize complex data. 
 
 (3) Comparison of physical characteristics of water produced. 
 
 (4) Amounts of water producible by wells. 
 
 (5) Comparison of fluid levels. 
 
 (6) Bridges and plugs of cement or other impervious material. 
 
 (7) Dyes or colorless substances for tracing underground flow of 
 water. 
 
 (8) Packers used in casing or in formation. 
 
 (9) Muddy water to indicate point of entry. 
 
 (10) Relation of sequence of wells "going to water" to geologic 
 structure. 
 
 (11) Comparison of chemical analyses of waters. 
 
 (12) Oil and emulsions accompanying water. 
 
 When water appears after a well has been producing clean oil, it is 
 usually more difficult to determine its source than at the time of a test 
 of shut-off, because the possible sources of the water have increased. It 
 is one thing to determine through what channel or stratum water is en- 
 tering a well, and another to ascertain how the water came to be in 
 that particular stratum. When water is native to a certain stratum, it 
 is here called "primary water;" when it obtains access through the 
 agency of a well, to other formations, it is termed "secondary water" with 
 respect to those formations. The waters of the typical oil field can be 
 classified with respect to position under the three headings, upper, lower 
 and intermediate water. It is, therefore, possible, in general, that water 
 found in production may be from either of these sources and may be pri- 
 mary or secondary in character. The possible contributory combinations 
 of these six elements are many. In dealing with water conditions in a 
 group of wells, all of these possibilities may demand consideration. The 
 problem is probably best attacked by first paying attention to the wells 
 producing most water and having the highest fluid levels. In order to 
 make reliable comparison, each pumping well should be tubed near the 
 bottom and the lifting of the' fluid conducted under similar conditions. It 
 is safe to assume at the start and in the absence of more convincing data, 
 that the largest water producers, or the wells with highest fluid levels, are 
 the offenders. 
 
 An outline is given of the various means of determining the source 
 of water in oil and gas wells. In dealing with this phase of the subject, 
 general material was drawn from a paper entitled "Source of Water in Oil 
 Wells," which was written by the senior author and appeared in the Feb- 
 ruary, 1920, issue of "Summary of Operations" of the California State 
 Mining Bureau.
 
 26 EL DORADO, ARK., OIL AND GAS FIELD 
 
 (1) Formation, Production and Casino Records of Wells: 
 
 In order to save time and money in dealing with water problems, it is 
 necessary to assemble accurate and exhaustive data on each well and to 
 record these in convenient and readable form. Those in authority should 
 standardize as far as practicable for a given area the nomenclature of for- 
 mations encountered in drilling. It is desirable that the driller's designa- 
 tion of samples should be confirmed before the final log is made. With one 
 person determining all samples from several drilling wells on a property, 
 uniformity of formation names can be accomplished. For instance, drillers 
 in the same field often name the same formation differently. Some samples 
 which are inspected with different degrees of scrutiny and under vary- 
 ing conditions of moisture, light, etc., may give diverse impressions to 
 different people. 
 
 Without a uniform system of logging formations, it is, in the absence 
 of unmistakable markers, difficult to correlate the well logs. Errors in 
 correlation lead to incorrect methods of combating water troubles, and also 
 to non-uniform water shut-offs. By this means, top water behind a water 
 string may be allowed to enter any porous formation and travel through 
 this channel to a nearby well in which this porous formation is exposed 
 in the hole. 
 
 There is, as yet, no evidence that non-uniform shut-offs are responsible 
 for any water production at El Dorado. Such is not likely to be the case, 
 if the cement used has properly bonded with the casing and walls of the 
 hole, for 100 feet or so, above the shoes of the water strings. 
 
 The need for accurate figures for production of oil and water is too 
 often overlooked. Erroneous ideas concerning the source of water in pro- 
 duction are likely to be developed to the end of misdirected remedial 
 effort. This is particularly true when two or more wells produce into the 
 same tank. Suitable equipment for the accurate determination of amounts 
 of oil, water and emulsion produced by each well will be found a sound 
 business investment in many cases. 
 
 Full records of all casing put into and removed from each well should 
 be available for use in case of water troubles or abandonment. The amount 
 and location of any side-tracked and perforated casing should also be re- 
 corded. Side-tracked casing may be left in such a position and condition 
 as to afford a passageway for water down past a shut-off point or upward 
 past a plug or bridge, and thus prevent a determination of the true source 
 of the water. 
 
 (2) Graphic Means to Visualize Complex Data: 
 
 In dealing with oil field problems, it is important to know the under- 
 ground structure and to obtain all possible information relative to the oc- 
 currence and production of oil, gas and water. Ambrose* has pointed out 
 that the best use of field data can be made when presented in graphic 
 form, by cross sections, underground contour maps, production curves and 
 peg models. 
 
 Until the geologic structure is accurately known, it will not be ap- 
 parent where to make the water shut-offs in order to establish a strati- 
 graphic uniformity. Peg models and cross-sections are used especially to 
 determine structure and to indicate sources of water due to haphazard 
 drilling campaigns. 
 
 With the aid of models and sections, the location of water that may 
 lie in or below the oil measures can also be determined with more or less 
 accuracy and drilling governed accordingly. 
 
 The comparison of the behavior of neighboring wells often gives cri- 
 teria regarding underground connections and source of water. Charts that 
 show graphically the average daily amounts of oil and water produced by 
 each well during each month, and the number of days the well produced 
 during the month, together with the reasons _ for anv non-producing days, 
 are valuable to indicate the effect of certain conditions or operations at 
 one well upon the production of another. 
 
 In considering the data of more than two wells, the problem becomes 
 complicated and graphical representation of data is necessary, in order to 
 make a reliable study of the several features, such as time and volume 
 of producible water. 
 
 *Afnbrose, Undcriiroiuid Conditions in Oil ! : ii'lds. liuU. /Q.I I". S. H urea it 
 Mines, .^. >6-fiS.
 
 EL DORADO, ARK.. OIL AND GAS FIELD 
 
 (3) Comparison of Physical Characteristics of Water: 
 
 The easily distinguishable non-chemical properties of water, such as 
 taste, temperature and odor, are often serviceable in indicating source of 
 water entering a well. If one or more of these properties are known 
 for the different waters encountered in drilling a well, an idea of the 
 source of the water appearing in production can sometimes be had. It '"s 
 usually not practicable to observe these conditions, due to the contamina- 
 tion of added water, or of new water encountered in the well, or due to 
 rotary drilling. However, it is well to note, when possible, the taste. 
 Temperature and odor of first water or its resultant combination with 
 other waters cased off behind a water string. The value of this feature 
 is greater when the well is drilled "dry" with cable tools or when no 
 drilling water whatever has to be added from the surface. 
 
 Ordinarily, the hotter water comes from the deeper levels. Water that 
 is salty to the taste usually comes from deeper levels than fresher water. 
 Sulphur gas is the principal source of odor in water, and its presence can 
 be substantiated by its blackening effect on silver. The writers have not 
 noticed any sulphur water at El Dorado. 
 
 Although such observations for a particular well may indicate that tlie 
 well is making top water, it would' remain to determine whether top 
 water was entering the productive formations as a result of the faulty 
 condition of some other well. Similarly, it should be determined whether 
 any supposed lower water was of secondary origin. 
 
 (4) Amounts of Water Produced by Wells: 
 
 The terms "amount" and "quantity" used here refer To actual volume 
 rather than percentages. Often in groups of producing wells, the well 
 which makes the most water can be singled out as the probable offender. 
 This is true of pumping wells when they produce all of the fluid that 
 comes into the hole. 
 
 Stratigraphically non-uniform shut-offs may make it difficult to des- 
 ignate the well letting water into the oil sand. Due to a low shut-off, well 
 Xo. 1 may allow considerable top water to infiltrate into the production 
 of well No. 2. Well No. 2 may thereby become the largest water producer 
 of a group of wells, but could not rightly be called the offending well. On 
 the other hand, well No. 1 may produce the least water of the group and 
 its status would have to be determined by other means. 
 
 The amounts of water produced by pumping wells are of little sig- 
 nificance in indicating the source of water when the fluid levels are con- 
 Tinually and uniformly high. In such cases, the productions do not rep- 
 resent the fluid capacities of the wells and the amounts of production ob- 
 viously depend then on such features as size of pump and tubing, efficiency 
 of pump, length of stroke and number of strokes per minute. It is evident 
 that under such conditions the offending wells may be producing less 
 water than a well or wells not letting water into the sand. 
 
 An increa c e or decrease in the amount of water a well produces is 
 an important item to consider for indicating the source of the water. The 
 sudden appearance of considerable water in a well or wells would indi- 
 cate possible sources, and these would be dependent largely on the con- 
 ditions obtaining in that area. Under average conditions such a sudden 
 increase of water would appear. more likely to be due to causes imme- 
 diately connected with the well itself. 
 
 A sudden increase in water production would point to such things as 
 a sudden development of large casing leak; the failure of shut-off; the 
 breaking in of water through thin formation or past a plug in the bot- 
 tom of the well; or the water pressure overcoming the effect of oil and 
 gas pressure. It is quite possible also that edge watrr or water due to 
 the drilling or to the fault of some other producing well, could manifest 
 itself suddenly when conditions of porosity are i'avorable. 
 
 After conditions have been remedied in the well in question, or in 
 neighboring wells, it may require considerable time to exhaust the accu- 
 mulated secondary water from the formations. The rate of exhaustion 
 would, of course, depend again on the porosity of exposed strata. A 
 aradual decrease in amount would indicate that the water was lej: into 
 the sand, and not native to it.
 
 28 EL DORADO. ARK., OIL AND GAS FIELD 
 
 (5) Comparison of Fluid Levels: 
 
 Fluid levels may be classified as follows: 
 
 (1) Those compared on a basis of distance from sea l?vel will be 
 
 termed "absolute." 
 (2) Those compared with reference to distance from a stratigraphic 
 
 horizon or stratum will be termed "stratigraphic." 
 
 High fluid levels usually indicate large productive possibilities of oil 
 or water. They also indicate the offending wells when the fluid level is 
 due to an excess of water. It is out of the ordinary to find a condition, 
 for a group of wells with settled production that have 'gone to water, 
 whereby the offending wells would not show the highest fluid levels. This 
 is noticeable in several cases at El Dorado. Exceptions to this general 
 rule are found when water is entering the lower portion of a well and is 
 restrained from seeking its own level in that well by a bridge or by a 
 plug, the lower portion of which was defective. In such cases, the con- 
 fined water will travel across to other wells through any porous strata 
 available. In an area of markedly inclined strata; water which enters a 
 well at any point may be conducted rapidly away by an unsaturated or 
 partially drained porous stratum to another well^ and the conditions of 
 porosity may be such that the secondary water will attain a higher strati- 
 graphic fluid level in the down-dip well. 
 
 The fluid levels should be taken, when possible, for idle as well as 
 for producing wells. It is, of course, necessary to obtain these 
 data under similar conditions for the different producing wells. 
 The levels should be taken at a certain time after produc- 
 tion was stopped. It is also advisable to conduct an investigation of 
 fluid levels after a period of uniform producing conditions for all wells 
 has elapsed. If a well has been pumping only a few days after a con- 
 siderable period of idleness, the figure obtained may be misleading. It is 
 apparent that an idle well will probably have a high fluid level. If its 
 level is considerably higher than those of neighboring wells, it should be 
 made the object of further investigation as, under ordinary circumstances, 
 such a condition could not exist in a non-offending well. 
 
 A comparison of fluid levels should be considered on the same strati- 
 sraphic plane, although if the formations have a gentle dip, sea level 
 basis will usually suffice. The greater the resistance to the passage of 
 water from one well to another, the greater will be the difference in fluid 
 levels of the offending and non-offending wells. 
 
 When infiltrating water travels up the dip of fairly steeply inclined 
 beds, a stratigraphic comparison of fluid levels will tend to exaggerate 
 the comparison, because the up-dip non-offending well could never attain 
 the same stratigraphic fluid level, due to water pressure, as the offending 
 down-dip well. The opposite is, of course, true when the water travels 
 down the dip. 
 
 It is felt that the operators in El Dorado have not studied fluid levels 
 to the extent that should be done and it is believed that such a study 
 would often be helpful in determining the repair of wells. The preceding 
 data on fluid levels was given in considerable detail in the hope that 
 such information might be useful in later work in this field. 
 
 (6) Bridges and Plugs of Cement or Other Impervious Material: 
 
 Ihe terms "bridge" and "plugs" are sometimes used synonymously. 
 "Bridge" is here used when the impervious filling is not in contact with 
 the bottom of the well; while "plug" designates a filling, part of which is 
 imnervious, which is in contact with the formation at. the bottom of the 
 well. 
 
 The proper manipulation of bridges and plugs of cement is frequently 
 employed and is one of the most reliable means of determining source 
 of water. If plugging the bottom of the hole shows that the water has 
 been entering the well at that point, the demonstration may constitute 
 the remedy. 
 
 If a studv of all available information does not sufficiently indicate the 
 point of entry of water in a well, the following is a proposed outline of 
 work: 
 
 (a) Retest the shut-off by placing a substantial cement bridge under 
 the shoe and conduct a bailing test. It often happens that a bridge does
 
 EL DORADO, ARK., OIL AND GAS FIELD 29 
 
 not form a water-tight bond with the walls of the hole, in which case 
 water may come from' below. If the bridge is tight, water may come 
 from defective casing, defective shut-off, or from any porous formation 
 existing between the top of the bridge and the shoe of the water string. 
 The general conditions governing such a test -are outlined in the previous 
 discussion of original tests of shut-off (pp. 19-21). 
 
 (b) If water is found to be entering the well above the bridge, re- 
 test the casing for leaks. 
 
 (c) If test (a) shows that the well still makes water, or does not 
 account for all of the water that was being produced, the bottom of the 
 well may be plugged with cement for a certain distance. After the 
 cement has set, a bailing test should be made. If the well still makes 
 water, continue plugging and testing in stages until the source of the 
 water is determined and the water is shut off. 
 
 (7) Use of Dye or Colorless Substance for Tracinq Underground Flow of 
 Water: 
 
 Suitable dyes can sometimes be used to good advantage for indicating 
 underground fluid connections and the direction of movement. Dye can 
 also be used for testing the efficiency of a water string. 
 
 The World War has greatly retarded the use of dyes since 1914, duo 
 to scarcity and prohibitive prices. Varying degrees of success have ac- 
 companied experiments in connection with oil field conditions. Some dyes 
 are decolorized by the reducing action of petroleum compounds and by 
 hydrogen sulphide, or are absorbed by mud and formations. Such dyes 
 are usualy unsuitable for oil well purposes. 
 
 The subject has not received the attention it merits, and it is be- 
 lieved that experimental work would point to a means of using dyes more 
 advantageously in tracing water. Some of the dyes that are absorbed 
 or reduced by crude oil may be used successfully when the fluid carries a 
 large percentage of water. 
 
 It is said that the dye eosin is not affected by hydrogen sulphide, 
 nitric acid, magnesium sulphate, sodium hydroxide, alcohol or gasoline. 
 The price and supply, however, prohibit its use at present. 
 
 The United States Geological Survey has used fluorescein for tracing 
 the flow of underground waters in connection with water supply problems. 
 It is said to be a delicate dye which is only slightly affected by the nor- 
 mal ingredients of natural waters; to be decolorized by acids and affe-cted 
 by some forms of unstable organic matter. A loss of color due to acidity 
 can be restored by making the sample alkaline. Stabler* points out that 
 fluorescein can be noted with the eye in solutions as weak as one part 
 in 40,000,000 parts of water and that one part in 10.000,000,000 can be de- 
 tected with the aid of a long glass tube. He considers it the most effi- 
 cient dye for tracing underground flow r s of water. In a personal inter- 
 view, Mr. Stabler stated that this dye can be obtained from the Eastman 
 Kodak Company, Rochester, N. Y., at a price of about $10.00 per pound 
 and that, regardless of its price, it is probably the most desirable dye 
 to use. 
 
 The chemical nature and intensity of a dye will influence the amount 
 that should be used for a given set of conditions. In testing the elTiciency 
 of a water string, two to five pounds of good dye would probably suffice, 
 while for use to show underground flow, ten pounds or more wou!d be 
 advisable. When testing a water string, the dye is put behind such casing 
 and washed down with a stream of water. The pumping of the well 
 should not be suspended. The appearance of dye in the production will 
 indicate a casing leak or defective shut-off. When testing for under- 
 ground connection, the dye should be released at the bottom of the sus- 
 pected well and this well should remain shut down during the time of 
 test. It is important to remember that dye placed in the bottom of well 
 No. 1 and showing in well No. 2 is not conclusive proof that well No. 1 
 i^ at fault. The current of water, flowing in the general direction No. 1- 
 No. 2, may be due to imperfections in one or more other wells. 
 
 ~*S fabler. Herman (Chief Engineer. Land Classification Board. [\ S. Geo- 
 logical Surrey), Engineering Investigations. The Reclamation Record (Depart- 
 ment of the Interior) J'ol. '/*, Xo. .?. March. 19?!.
 
 30 EL DORADO. ARK.. OIL AND GAS FIELD 
 
 It is stated by A. W. Ambrose, chief petroleum technologist of the 
 Bureau of Mines, that "acid orange" is a cheap and reliable dye for 
 average sub-surface conditions. The cost or this dye is about 90 cents 
 per pound and is obtained from Hemingway & Company, New York. A 
 Prussian blue is reported to have been successfully used in a number of 
 cases, and it seems to meet the general requirements of oil field condi- 
 tions. It is a cyanide of iron, and the writers are not fully advised as 
 to the effect that sulphur compounds may have upon it. It is, however, 
 probably one of the most reliable and available dyes for present use. 
 
 It is understood that the underground flow of water has been traced 
 by colorless substances which the water did not originally contain except 
 in comparatively small quantities. For instance, one of the rare elements, 
 such as lithium, may be added in small quantity and samples from some 
 other point tested by spectroscopic analyses. Or an excess of .a com- 
 pound, such as chlorides or sulphates, may be added and the samples 
 tested by measuring the resistance to an electric current, or by chemical 
 means. 
 
 (8) Packers Used in Casing or in Formation: 
 
 Packers run into the wells on tubing or casing and set in casing or 
 formation are used to good advantage for testing the source of the water. 
 The packer is supposed to form a tight bond between the wall of the 
 hole or the inside of the casing and the tubing or casing on which it is 
 set and thus retards the fluid moving past the point at which the packer 
 is set. The subsequent testing by bailing or pumping is done below the 
 packer, whereas in the case of a bridge, the reverse is true. 
 
 A packer is usually employed for testing and Avith the idea that if it 
 excludes the water, it will remain in the hole. The common packer makes 
 use of an expanding rubber or canvas to effect a seal. Although the rub- 
 ber is decomposed in time by oil and water, such packers have frequently 
 been left in wells of other fields for permanent correction of water trou- 
 bles. Hemp has been used successfully in this connection, and will prob- 
 ably last longer than rubber. The efficiency of a packer may sometimes 
 be increased by caving formation or by the addition of mud or sand put 
 in from the surface. Experience has shown in some fields that packers 
 should not be used against the formation, if a permanent water shut-off 
 is to be expected. 
 
 (9) Use of Muddy Water to Indicate Point of Entry: 
 
 The point of entry of water into a well may sometimes be determined 
 by using thin mud fluid or muddy water. The well should be filled as 
 high as practicable with muddy water, with the hole open to bottom or 
 otherwise. The fluid should then be bailed off the top and a careful watch 
 kept to note the thinning of the mud and the appearance of clear water. 
 As the fluid level is lowered in the hole, the head of infiltrating water will 
 again over-balance the fluid column in the well, with the result of thin- 
 ning up the mud with clear water. As soon as the bailer has reached the 
 point of inflow, it will pick up practically clear water. The point of in- 
 flow is thereby approximately located. 
 
 (10) Relation of Sequence of Wells "Going to Water" to Geologic Struc- 
 ture: 
 
 Water which occurs in the down-dip portion of an oil-bearing stratum 
 is called "edge-water." As the oil is removed by producing wells, the 
 water will replace it. The head of the encroaching water will be a lac- 
 tor in its rate of progress, as will the off-setting oil and gas pressure. In 
 strata of low inclination, such as at El Dorado, the line of encroachment 
 will be quite irregular and will be controlled largely by the poresity and 
 texture of the edge-water sand. 
 
 The classification of a water as edge-water would usually be based 
 solely upon the evidence, of down-dip wells going to water first. The 
 available means of determining the stratum through which encroachment 
 is taking place are not usually different from those described 'elsewhere 
 for locating the point of entry of water into a well. It may occasionally 
 happen that a clue is readily available owing to the fact that rrome of the 
 down-dip wells are not as deep stratigraphically as the others. This con- 
 dition would probably eliminate, some of the strata as edge-water-bearing 
 possibilities.
 
 EL DORADO, ARK.. OIL AND GAS FIELD 
 
 (11) Comparison of Chemical Analyses of Waters: 
 
 It has been demonstrated that a careful investigation of numerous 
 chemical analyses will usually disclose identical characteristics of the 
 waters of each horizon; and that these characteristics are apt to persist 
 in general over the area of an oil field. It is reasonable to assume that, 
 if the waters of different depths are restrained from mixing, differem 
 conditions will obtain and render them dissimilar. Some of the controlling 
 factors affecting the mineral contents of the water are temperature, pres- 
 sure, time of contact with formation, distance traveled through forma- 
 tions, chemical nature of the reservoir formations, quantity of water, ana 
 the accessibility of meteoric water to the point of sampling. The best 
 results from water analyses can be expected where the structural move- 
 ments have not permanently destroyed the impervious character of inter- 
 zonal formations. The intermingling of waters along fault planes and 
 through crushed zones will, of course, minimize the possibility of a defi- 
 nite conclusion from analyses. 
 
 Chemical analyses have been used in several fields to determine the 
 source of the water produced by oil wells. This work has shown that the 
 engineer can not use analyses of one field as an indication of the chem- 
 ical properties of the water of another field. Any attempt to use chemical 
 analyses of waters at El Dorado must be carried on as an investigation 
 entirely independent of the findings in other fields. Samples of water 
 from definite, known sands should be analyzed and then later when a well 
 makes water whose source is unknown, a sample can be collected for 
 analysis. The analysis of this water can then be compared with the 
 known samples, so as to determine the origin of the water. 
 
 Analyes of Underground Waters of the El Dorado Field: 
 
 Table No. 4 gives the results of analyses of four samples of water 
 from El Dorado wells (probably edge or so-called bottom water) and of 
 two samples of known top water from shallow water wells. The analyses 
 were made by W. F. Fulton of the Louisiana Oil & Refining Company at 
 Shreveport, Louisiana, and by W. B. Lerch of the U. S. Bureau of Mines 
 at Bartlesville, Oklahoma. 
 
 Lack of time . prevented a complete collection of water and compila- 
 tion of their analyses. The few samples examined showed a very marked 
 difference in the chemical properties of upper and lower waters. The gen- 
 eral differences adhere rather closely to the differences in waters of some 
 other fields as pointed out by Rogers* The difference in total solids is 
 the most notable and it has an important influence on the percentage 
 figures shown in Table No. 4. For instance, the first analysis shows 48.52 
 per cent chlorine and the last shows 40.01 per cent. There is, however, 
 about 628 times more chlorine in the first sample (bottom water) than in 
 the last (top water). The samples of top water were taken from com- 
 paratively shallow depths and the character of any deeper top water is. 
 therefore, uncertain. Because all wells have been drilled with rotary 
 tools, it has been impossible to obtain any samples of lower top waters. 
 The bottom or edge water at El Dorado has a distinctly salty taste. The 
 facr that the large producers of water also make water with a similar 
 taste indicates that the large water producers are making edge or bot- 
 tom water. As remedial work is undertaken, chemical analysis may be 
 found useful. 
 
 (12) Accompanying Oil and Emulsion: 
 
 When water and oil are intimately mixed by 'agitation, an emulsion is 
 formed. It is known to be formed by such conditions as the sudden ex- 
 pansion of gas in the presence of oil and water and by the passage of 
 oil and water through small openings, such as leak-back past a worn "bnl?. 
 and seat of a pump, between tight-fitting liner or screen and oil string., 
 past defective bottom plug and. through the oil-bearing formations. It ap- 
 pears likely that emulsion may be formed at the surface as well as un- 
 derground. 
 
 *Rt>f/e>'s, G. S., Chemical Relations of the OH Field ]\'atcrs in San Joaquin 
 l-'nllev, Calif nrnin. II. S. G. S. Bull. 6si. IQI?. '
 
 EL DORADO. ARK., OIL AND GAS FIELD 
 
 
 
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 EL DORADO, ARK., OIL AND GAS FIELD 33 
 
 Association of Oil and Water: 
 
 A correct idea of the underground relation existing between the oil 
 and water appearing in production, is essential to establish the best prac- 
 tice for the removal of the maximum amount of oil and gas. In studying: 
 this phase of the subject, the evidence was found to be rather meager on; 
 account of poor logging or slight distance drilled into the oil sand. 
 
 Plate VII was constructed from thirty-eight well logs for the purpose 
 of estimating the character of the oil and water zones. Plate IV was pre- 
 sented to generalize the conclusions drawn from information at hand. 
 
 The north-south generalized section of Plate IV represents conditions- 
 along the high portions of the structure and also the variance in certain 
 features from north to south. The convolutions of the strata represent 
 saddles along the axes of the structure. It is assumed that the oil zone 
 proper is free from edge water along the higher portion. The dip is ex- 
 aggerated fifty times in both sections, the horizontal scale being 1,000 feet 
 to the inch and the vertical scale being twenty feet to the inch. These 
 scales are used for proportioning the thickness of sand and its change in 
 elevation, but the remaining features are necessarily generalized. 
 
 The fault shown in Plate IV is assumed for the reason that it makes 
 a rather sudden change from productive to practically non-productive ter- 
 ritory, and from light oil to heavy oil. 
 
 The oil sand proper varies in texture from sand to sandy shale and in 
 thickness from about sixteen feet at the north end to about ten feet at 
 the south end. The sand is less prolific in some parts of the field than 
 in others. The logs show that a hard cap rock, one to two feet in thick- 
 ness, is encountered uniformly just above the oil sand in the north end 
 of the field. South of about the middle of Section 8-18-15. such a cap rock 
 is not generally logged. It appears likely that a hard rock layer does not 
 overlie the oil sand in the southern portion of the field and that some of 
 the wells, logging a cap rock, have encountered the lower cap rock in- 
 stead. A cap rock below the oil sand proper appears to persist through- 
 out the field. Below this cap is a zone of variable texture that appears to 
 carry both oil and water. Deposits of oil have been retained under the 
 highest portions of the persistent second cap rock and in places appar- 
 ently under local impervious partings. 
 
 Below the second zone, which is about twenty feet thick, a third cap 
 rock was logged in a number of wells, under which occurs another sandy 
 zone that carries salt water. The sands between the first and third cap* 
 rocks are usually designated in the well logs as the oil sand. 
 
 Wells that are drilled just into the sand, below the second cap roclc 
 on high points of the structure, may make clean oil if they are suffi- 
 ciently controlled (i. e., their flow restricted) to avoid water coning. 
 Wells located far down on the structure within range of edge water, 
 should also produce clean oil if drilled only a few feet into the main oil 
 sand and restricted so that they will not produce too fast from the bot- 
 tom of the sand. The east-west section of Plate IV illustrates the un- 
 derground conditions to be dealt with. 
 
 Some operators believe that the lifting of excessive water must be 
 taken as a matter of course in cases of this kind. In the higher por- 
 tions of the structure, there was probably little or no water originally 
 in the first oil zone. As the pressure was reduced and oil removed, edge 
 water encroached further up the dip. Moreover, when wells are drilled 
 far enough down slope, edge water may easily be drawn into them from 
 the bottom of the sand, if they are pumped hard or allowed to flow full 
 capacity, even though they have barely penetrated the oil sand. 
 
 In this field, when the top of the oil sand lies as low as 1,935 feet 
 below sea level, the sand should be barely touched when drilling in and 
 the output restrained considerably below the full capacity of the well. 
 This should not be interpreted to mean that wells in which the oil sand 
 was found at shallow depths below sea level, such as 1,930 or 1,925 feet, 
 can be drilled deep into the sand and "pulled hard," without danger 
 of drawing in edge water. All high-pressure wells must be controlled in 
 this field, not only to avoid the "drawing in" of edge water, but to pre- 
 vent them from drilling themselves deeper into the soft and consoli- 
 dated sand body.
 
 34 EL DORADO. ARK.. OIL AND GAS FIELD 
 
 Thus the evidence indicates that clean production can be expected 
 from wells that are fairly high on the structure, that are drilled only a 
 few feet below the top of the oil sand and that are kept under proper 
 control. Exceptions to this rule would be due to the letting in of water 
 by neighboring wells or the production of top water. 
 
 The wells shown in Plate IV are hypothetical wells, drawn to repre- 
 sent the following conditions which exist in various parts of El Dorado 
 field: 
 
 Wells A and I: Low on the flanks of the structure. Drilled too deep 
 or produced too rapidly, resulting in the drawing in of edge water. 
 
 Wells B and G: Bottom of hole rather close to edge water level in 
 the sand, but can produce large quantities of clean oil by "pinching 
 down." 
 
 Wells C, M and S: Drilled too -deep and penetrated second sand at 
 points where it carries water. These wells are flooding the upper produc- 
 tive sand with water. 
 
 Wells D, F, N and R: Drilled to proper depth and cased properly, but 
 making water let into the sand by other wells. 
 
 Well E: Drilled through third cap into bottom water, plugged back 
 but not high enough to catch second cap, flooding oil sand with water. 
 
 Well H: Low on structure and originally made edge water. Plugged 
 part way back to cut off entrance of water. This well should make con- 
 siderable oil if properly controlled. 
 
 Well J: East of probable fault, oil low gravity and a great deal of 
 water, entered deposits of heavy oil, non-commercial at present. 
 
 Wells K, P and T: High on structure, producing clean oil and no 
 water. 
 
 Wells L and U: Drilled through second cap rock, but properly plugged 
 to exclude water. 
 
 Wells O and V: Drilled just below second cap into underlying oil on 
 structural highs, produced too rapidly, causing water coning. 
 
 Well Q: Drilled into bottom water and not plugged, flooding oil sand. 
 
 In the case of Well'N, it will pay to plug with cement to a point sev- 
 eral feet above the contact between the water and oil, providing the sand 
 is reasonably consolidated. If water with a high head has access to a 
 hole, the water will soon prevent the entry of oil into the hole. Where 
 there is no parting between the water 1 and oil, a plug cannot be expected 
 to hold the water back indefinitely. However, the water cannot enter the 
 hole as freely as in the case of open hole, because it must pass upward 
 through a greater thickness of formation, with a resulting increased re- 
 sistance from the formation. In doing so, some of the oil is pushed ahead 
 of the water, also the oil has a longer period lor draining laterally into the 
 hole which often results in an increased extraction of oil. 
 
 An example of the harmful effect that an improperly drilled well can 
 have on a correctly drilled well, is here given. In El Dorado, Well A was 
 drilled too deep with rotary and produced a large amount of salt water 
 with the oil. Well B, about 300 feet away, was carefully finished about 
 one foot below the top of the oil sand with cable tools shortly after A 
 came in. Well A had been flowing an oil-water fluid vigorously and B also 
 flowed oil for a short time. Muddy salt water then appeared in B, which 
 was strong evidence that rotary mud and water had entered from A, as 
 these two wells were practically isolated at that time. The flow in B 
 quickly subsided and it was then pumped. The oil production was, com- 
 paratively small and the water continued to appear in large quantities. 
 Neither Well A nor B will show a profit unless A is repaired properly and 
 promptly. 
 
 Use of Cement 
 
 In the history of the oil industry, many methods have been devised 
 for the exclusion of water. For shutting off top water with casing, the for- 
 mation shut-off, seed bag or other material that will swell behind the pipe, 
 tamping method, various types of packers, mud-fluid in combination with
 
 EL DORADO, ARK., OIL AND GAS FIELD 35 
 
 formation shut-oft's, and cement have been used. For bottom water, the 
 tamping of various substances, mechanical plugs and cement (sometimes 
 in combination with mud) have been used. Of these several methods of 
 excluding water, in many cases, cement has proved to be highly satisfac- 
 tory for both classes of work. Mud fluid is in many fields of considerable 
 use, particularly in top water shut-offs. It is not serviceable when used 
 alone for high-pressure bottom water. It is often necessary to use me- 
 chanical devices or mud-fluid in connection with cement for the purpose of 
 clogging porous formations and stopping the movement of water, oil or 
 gas. 
 
 The use of cement behind water strings has been quite diverse in ap- 
 plication. Detailed descriptions of cementing methods have been de- 
 scribed by Tough.* 
 
 A brief description of the various ways of cementing in different fields 
 is here given. Cement has been placed behind casing (1) by dumping it 
 outside of the casing at the surface; (2) by lowering the casing into the 
 mixed cement which has been placed at the bottom of the hole and effect- 
 ing no change in the height of the cement inside and outside the casing; 
 (3) by placing the cement in the bottom of the hole by pouring it in dry 
 or mixed, or with a dart bailer (adapted) or dump bailer and then lower- 
 ing the casing into the cement with a plug in the bottom of the casing or 
 with a head on top, having the casing full of water, thus leaving little or 
 no cement in the shoe joint; (4) by pumping the cement through tubing, 
 with or without the aid of one or two wooden plugs to determine the 
 travel of the cement, following with water or mud, and using a packer at 
 bottom or a packing head at top; (5) by pumping cement through the 
 casing and following it with water or mud, using no plugs to determine the 
 travel of the cement and to prevent its mixing with other fluids; (6) by 
 the same method as number 5, except using one plug after the cement; (7) 
 by the same method as number 5, except using one plug before and one 
 plug after the cement. 
 
 Method 1 is unreliable and has not been attempted to any extent. In- 
 deed, the conditions allowing its use are not frequently met. Method 2 is 
 not reliable, especially for rotary holes, because there is little or no -clean- 
 ing action on the walls by the cement. The more cement that is used, the 
 more it is necessary to drill out. In method 3, good work has been done 
 with the dump bailer, using small amounts of cement, but it is not suitable 
 for rotary holes, unless the formation will stand washing, on account of 
 probable inability to properly free the walls of mud with a large amount 
 of cement. Method 4 has been used to good advantage, especially when a 
 small quantity of cement or a quick-setting cement is used. The cement 
 can be put away in quicker time with tubing than with casing. The 
 method, however, is now practically obsolete for casing jobs. Method 5, 
 although used in some fields, is not considered reliable, as there is danger 
 of diluting the cement or of leaving too much cement in the casing. By 
 method 6, it becomes known when the cement is all out of the casing, but 
 unless a large quantity of cement is used, the excessive dilution of the 
 first of the cement column may render the work unsuccessful. Method 7 
 is considered the most reliable cementing practice that has been developed. 
 There are various modifications of this practice, but in principle the first 
 plug prevents the dilution of the cement with the fluid in the pipe and 
 allows its passage after that plug reaches bottom, while the second plug 
 protects the upper part of the cement column and indicates when the 
 cement is all out of the casing, by stopping or slowing the pump. The 
 first plug remains in the bottom of the casing and the last plug cannot 
 leave the casing. The most efficient plugs are made of wood with circu- 
 lar pieaes of belting to fill out the full diameter of the pipe, except that 
 an inverted leather cup should be placed on top of the second plug. 
 
 Probably the most improved practice in connection with the two-plug 
 system of cementing water strings is found in the patented Halliburton 
 and Perkins methods. In the former, the exact position of the last plug, 
 which follows the cement, is always known by reading a steel tape. The 
 
 *Tough, F. B., Methods of Shutting off Water in Oil and Gas Wells, Bul- 
 letin 163, U. S. Bureau of Mines, 1918.
 
 36 EL DORADO. ARK., OIL AND GAS FIELD 
 
 tape is attached to the plug, runs through a packing device and is fed from 
 a reel and over a pulley. This apparatus is coming into extensive use in 
 various fields of the country, particularly in southern Oklahoma. A full 
 description is given by Swigart and Schwarzenbek.* The position of the 
 plugs is checked by reading a water meeter. 
 
 At El Dorado the general practice has been to use only one wooden 
 plug with a sack of shale placed on top of it, to follow the cement. The 
 sack of shale is meant to act in the same manner as an inverted cup, i. e., 
 stall the pump when the plug reached bottom. This practice, although ap- 
 parently successful, is not always as reliable as the two-plug method. 
 
 The use of a loosely-filled sack of fine shale following a plain wooden 
 plug, is no doubt an efficient method of stopping the pump at the end 
 point, provided the shale is retained in the sack. The sack may become 
 torn before it travels very far and the particles of shale separated from 
 the top of the plug. If this happens, circulation may obtain between the 
 plug and the casing, when the plug reaches bottom, and thus carry the 
 cement up above the casing shoe. As a matter of fact, if the plug is 
 almost the same diameter as that of the casing, the pumps will be slowed 
 up so appreciably when the plug reaches bottom, that it would be dis- 
 tinctly noticeable. 
 
 Because of the large amount of bottom hole plugging which will even- 
 tually have to be done in El Dorado oil field, a brief discussion of plugging 
 with cemeut will be included. Cement for bottom water jobs in other 
 fields has been handled in different ways; (1) by pouring dry or mixed 
 cement into the casing at the surface; (2) by placing mixed cement on the 
 bottom with a dart or dump bailer; (3) by dropping cement-filled metal 
 containers to bottom and breaking these up with the tools; (4) by pump- 
 ing cement through tubing and holding a pressure. Method 1 is almost 
 certain of failure. With Method 2, small quantities of cement can be suc- 
 cessfully placed on bottom with a dart bailer and more can be added if 
 some device is used to hold the dart open after it trips. The use 
 of a dump rod attachment injures the cement. The dump bailer is a 
 thoroughly reliable tool for such work and should always be used in pref- 
 erence 'to other bailers. Fig. 2 shows one of the common types of dump 
 bailer. This device can be used very successfully when the walls of the 
 hole to be cemented are fairly clean, when all gas, oil or water movement 
 has been stopped and when it is not necessary to force cement into the 
 pores of the formation. Method 3 has been used quite successfully in dif- 
 ferent fields. It offers opportunity for quieting very weak fluid movement 
 by the tamping effect and thus allowing the cement to set on top of the 
 tamp. It is a convenient method to try where apparatus for better 
 methods is lacking. 
 
 Method 4 is a very satisfactory way to cement off bottom water with 
 a high head. As shown, C of Plate III, the tubing is run nearly to bot- 
 tom of the hole through a casinghead packer, which has an outlet valve. 
 The tubing should first be run to bottom and circulation of mud started to 
 clean out collected debris. After circulation is gained, the cement is then 
 started through the pump with or without preceding it with a wooden plug. 
 When a plug is not used, the cubic contents of the tubing are calculated. 
 The progress of the cement can be checked by a water meter. In this 
 method it is important to know when the first cement reaches bottom and 
 it becomes impracticable to measure mixed cement from a tank. 
 
 If a plug is used, the pump will be checked when the first cement 
 reaches bottom, because the tubing is not held high enough to allow the 
 plug to pass entirely out. In any event, when the cement reaches bot- 
 tom, the tubing should be raised slightly above the renuired depth for the 
 top of the cement plug, and the outlet valve on the casing should be closed. 
 The cement is then forced against the walls of the hole and into the pores 
 of the formation. If the cement is readily absorbed by the formations, it 
 
 *Swigart. T. E., and Schwarzenbek. F. X., Petroleum Engineering in the 
 Hewitt Oil Field, Oklahoma Co-operatirc Report of State of Oklahoma and 
 U. S. Bureau of Mines, January, 1921. Distributed by Ardmorc Chamber o\ 
 Commerce. Price, $1.00.
 
 EL DORADO, ARK., OIL AND GAS FIELD 
 
 37 
 
 SPECIFICATIONS AND USE 
 
 1 - Make reins of ifinch square iron as far as 6 -inches below 
 
 the latch and f-inch square iron below that point, allowing 
 a larger space for filling with cement. 
 
 2 -Chains should be finch Swedish steel for 6|-inch, or small- 
 
 er, and f-inch material for larger than 6|-inch bailer. 
 
 3 -Chains should be fastened to removable eye-bolt which ex- 
 
 tends through the valve, facilitating repairs and transpor- 
 tation. 
 
 4 -Use only neat cement and fresh water, i.e. cement without 
 
 sand, rock or other material. 
 
 5 - Proper mix about 45 pounds water to 100 pounds cement. 
 
 6 -Mix thoroughly and rapidly. 
 
 7 -Just sufficient cement to fill bailer should be mixed at once. 
 
 8 - When lowering cement-filled bailer, run slowly enough to 
 
 avoid latch moving below bail and dumping cement above 
 bottom when slow motion is resumed. 
 
 9 -Care should be taken not to trip the latch when bailer hits 
 
 top of water. 
 
 10- A sectional bailer; made of several joints of pipe, should be 
 used when it is desired to dump a considerable quantity of 
 
 1 1 Before cementing, stop gas or water movement at cement- 
 ing point with a sufficient head of water, or with mud. 
 
 12 -Avoid dilution of cement, after opening valve, by holding 
 bottom of bailer at top of loose cement a sufficient time 
 to finish emptying cement from bailer. 
 
 13 -Cement should be allowed 10 days to set. Maintain a con- 
 stant head of water during that time. 
 
 a 
 
 U. S. BUREAU OF MINES 
 
 PETROLEUM DIVISION 
 DAI!AS, TEXAS. 
 
 SKETCH SHOWING 
 
 DUMP BAILER FOR 
 
 CEMENTING OIL WELLS 
 
 Drawn by J. G. Shumate Dare flr 11. 1921 
 Scale, Diggrammau 
 
 Fig. II. Dump Bailer, p. 102.
 
 EL DORADO. ARK., OIL AND GAS FIELD 
 
 is necessary to have enough in readiness to supply the needs of a predeter- 
 mined pressure or to know when the last cement has left the tubing. This 
 can be ascertained accurately by a wooden plug following the cement or 
 by reading a water meter, through which passes the water pumped into 
 the well. When the cement is all out of the tubing, the tubing is raised off 
 the plug, and the pumping is resumed with the outlet valve at the casing- 
 head partly open. Any cement that may have risen above the desired point 
 can be circulated out. Care must be taken to maintain a constant pressure 
 or otherwise the cement may not remain at rest and thereby fail to set. 
 
 In using the above method, it is obvious that the cement introduced and 
 followed by the second plug, may not be enough to fill up the cavity and 
 pore spaces under the desired pressure. In that event, more cement can 
 be added, followed by another wooden plug, after the extra water has been 
 circulated out of the way. It is obvious that a long plug in the tubing may 
 cause trouble in circulating out extra cement in case the formations would 
 take no more cement. 
 
 Plate VIII shows a crew making preparations to cement off bottom 
 water (through tubing) in Wood 119 of the Arkansas Natural Gas Company. 
 Notice both low-pressure and high-pressure pump in the foreground. 
 
 In view of the above and the fact that 2,200 feet of 2-inch tubing will 
 hold only about forty-eight sacks of cement, it would seem to be better prac- 
 
 Plate VIM. Preparing to Cement Well Under Pressure in Bottom. Arkansas 
 Natural Gas Company, Wood No. 199, Section 20-18-15, p. 110. 
 
 tice to omit the second plug. Then enough cement can be kept on hand 
 and mixed in time for continuous pumping in of the cement necessary. The 
 tubing should be kept full of cement until no more can be forced in, ?fter 
 which the circulating valve should be cracked and the extra cement cir- 
 culated out between the outside of the tubing and the inside of the casing, 
 at a sufficient speed to maintain a constant pressure on the cement in the 
 well. After a certain point is reached, the action of the pump will give a 
 good idea of about how much more cement will be taken. It is, therefore, 
 possible to reduce the waste of cement by starting mud or water into the 
 tubing somewhat before the end point is reached. The cost of the cement, 
 however, is of secondary importance. 
 
 Several wells in the El Dorado field that produced bottom water have 
 been plugged bv cementing through tubing under pressure, with satisfac- 
 tory results. The following wells were plugged either under the super- 
 vision or at the request of the State Conservation Department: 
 
 1. Foster Oil Company, Hinson No. 4, was plugged with cement 
 (amount unknown), which shut off the water. It then produced clean oil. 
 
 2. Guffey-Gillespie, Steadman No. 3, was plugged with cement (amount 
 unknown), which shut off water.
 
 EL DORADO, ARK., OIL AND GAS FIELD 
 
 3. Standard Oil Company, R.obertson "B" No. 3, was plugged with 
 thirteen sacks of cement, materially reducing the production of water. 
 
 4. Busey, Armstrong No. 1, was plugged with ninety sacks of cement 
 and shut off bottom water. This well has been abandoned. 
 
 5. Lucas Tomberlin, Crawford No. 1, was plugged with eighteen feet 
 of cement, for the purpose of abandonment. This work was done in co- 
 operation with the U. S. Bureau of Mines. 
 
 6. Magnolia Petroleum, Company, McKinney No. 3, was plugged nine 
 feet with cement, but the plug is now being drilled out. This well produced 
 oil for a short time after it was plugged. The cement may have shut off 
 most of the productive portion of the sand. 
 
 7. Constantin Oil & Refining Company, Hill No. 3, was plugged with 
 300 sacks of cement, for the purpose of abandonment. 
 
 8. Arkansas Natural Gas Company, Wood No. 199, was plugged by 
 stages with cement. The first batch of 160 sacks filled the hole only two 
 feet. There was 180 sacks of cement next pumped in, filling the hole three 
 and one-half feet. Then 120 sacks of cement was pumped in, making a 
 total of 460 sacks. After pumping in nine wagon loads of fine sand and 
 empty cement sacks, eighty more sacks of cement was added. This made 
 a total of 540 sacks of cement. Soon after this, the well started flowing oil, 
 but it soon drew in water, as no "chokes" were inserted in the flow line. 
 
 This well is reported to have been drilled only two feet below the top 
 of the oil sand. When first opened up, it produced about ten days through 
 a %-inch choke. The rate of now was even then too rapid, for large quan- 
 tities of sand and water were expelled, and the flow was finally cut off by 
 water. Measurements showed the well had drilled itself at least 
 two feet deeper. Probably it had drilled itself much deeper than 
 the measurements indicated and had subsequently filled in with loose 
 sand. The well is no doubt located where edge water occurs in the bot- 
 tom of the main oil sand, and, therefore, great care should have been exer- 
 cised in regulating its flow. The fact that the well flowed again after plug- 
 ging, illustrates the point that plugs are beneficial even when it is prob- 
 able there is no parting between the oil and water. If this well had been 
 sufficiently controlled after the plugging, there is little doubt that it would 
 have produced considerable oil. 
 
 Some wells were plugged by means of an improvised dump bailer with 
 a rod attached to the dart for dumping the cement. This method was 
 adopted because a regular dump bailer was not available. The washing of 
 the cement and its picking up in the return of the bailer to the surface 
 were minimized by first attaching only a few feet of dump rod. Additional 
 lengths were screwed on, as the cement filled up the hole. The idea was 
 to have the bottom of the bailer dump each time only a few feet above 
 the top of the cement. The engineers of the Bureau of Mines worked on 
 the abandonment of two wells: the Abner Davis, Cornish No. 1, and the 
 Crosby Syndicate, Jackson No. 1. The former was plugged with eight 
 sacks of cement which filled the hole about sixty-six feet, and the latter 
 was plugged up sixteen feet with cement. 
 
 Operators plugged the following wells by dump bailer method, result- 
 ing in increase of oil production and decrease of water production: 
 
 Hickman & Baird, McKinney A-l, plugged six feet with cement. 
 
 Hickman & Baird, McKinney A-2, plugged three feet with cement. 
 
 Hickman & Baird, McKinney 1, plugged nine and one-half .feet with 
 cement. 
 
 Hickman & Baird, McKinney 3, plugged with twenty sacks of cement. 
 
 White Oil Corporation, Armstrong N-2, plugged twenty-four feet with 
 cement. This well then made eighty-four barrels oil. Drilled out one 
 foot at a time, it then produced water. Plugged back second time, now 
 pumping sixty barrels oil, no water. 
 
 White Oil Corporation, Armstrong S-l, plugged with twenty sacks 
 cement and shut off bottom water. 
 
 It has been repeatedly proved at El Dorado, that proner plugging will 
 shut off or materially reduce the production of water, and because this is 
 the most important remedial work that can be done in this field it should 
 be concentrated upon by operators. 
 
 Some of the operators have had apparent success in excluding bottom 
 water by tamping empty cement sacks in the bottom of the hole with the 
 drill pipe. The sacks are rolled tightly, placed in the top of the drill pipe
 
 40 EL DORADO, ARK., OIL AND GAS FIELD 
 
 and are then forced to bottom by the pump. The sacks are wedged into a 
 very compact mass by "spudding"' the drill pipe on them. It is very doubt- 
 ful if the tamped sacks can be relied on to permanently retain sufficient 
 rigidity to hold back the water. The apparent success may be only tem- 
 porary. Time and an increasing differential between the water pressure 
 and the fluid pressure above the plug, is apt to wreck such a plug. 
 
 Handling of Cement: 
 
 The following is taken in part from "Engineers' Survey of Burkbur- 
 nett," Wichita County, Texas, by the present authors, appearing in the Oil 
 & Gas Journal, issues March 24 to April 20, 1922, inclusive. 
 
 Pure cement should be used and mixed with as little water as is pos- 
 sible for handling in the pump or bailer. It should not be unnecessarily 
 diluted with water or -with mud, after it is placed in the well. Cement is 
 a definite mixture of compounds, some of which are soluble in water. The 
 soluble portions should hot be separated from the insoluble. Therefore, a 
 diluting or "washing" of the cement will seriously, if not wholly, destroy 
 its hardening qualities. Likewise, a dilution with an excess of other ma- 
 terial, such as mud, will reduce its strength. 
 
 Cement will set readily under salt water and many other foul or highly 
 mineralized waters, providing sufficient care is taken in handling it. 
 
 Ten feet of settling through water is too much washing for a small 
 quantity of cement. The unsuccessful use of the ordinary bailer with a 
 rod attached to the dart, which adaptation was originally designed for 
 dumping drilling water, has led many operators to assume that cement will 
 not set in oil field water. It has been proven that the dump rod is the 
 cause of many failures, due to the washing of the cement while settling 
 through the water from the dart to bottom. 
 
 The cement should be placed directly from the bailer at the bottom 0? 
 ^the hole with as little agitation as possible. This can be done by a suitable 
 
 dump bailer, such as is shown in Figure 2. It will pay an operator to 
 possess a reliable tool of this kind, if he expects to use that method for 
 
 -cementing casings or for plugging off bottom water. Some of the patented 
 dump bailers are dependable; one makes trips and holds the valve open 
 
 "."by means of a latch near the bottom. 
 
 After the first bailer is dumped, care should always be taken to raise, 
 the bottom of the bailer to the top of the cement and allow ample time 
 for draining the cement from the bailer, for, otherwise, the cement will 
 
 drain from the bailer as it is drawn upward. This is undesirable, because 
 it means a considerable settling of the cement, through the water. It should 
 
 "be made certain that all commotion, such as action of gas or water, is elim- 
 inated before the cement is placed, or very shortly thereafter. 
 
 When cement can be made to bond with the walls of the hole, there is 
 no better method than a good cementing job for shutting off top water with 
 casing or for plugging off bottom water. When handled properly, it will 
 set under nearly all conditions; in foul water and in oil. Age, moisture 
 and improper storage may render a good quality of cement unfit for use. 
 Failures of cement to set in oil wells have resulted from poor cement, and 
 these can probably be prevented by the use of simple tests made in ad- 
 vance. The following procedure is recommended: Take three small av- 
 erage samples of the cement; mix one with water from the well, and the 
 other with distilled or very pure water. Place the stiffly mixed samples in 
 tall containers and finish filling the first two with the foul water, taking care 
 to avoid commotion and washing. On the third sample, the same water 
 may be added to the container that was mixed with the cement. After a 
 day or so, notice the condition of the samples. If none of them have set 
 hard, experiments should be made with other lots of cement until it is 
 certain that a reliable lot has been found. 
 
 It is common practice, in some fields of other states, to use from 100 
 to 500 sacks of cement and to pump it through casings with or without the 
 use of separating plugs. In some of these instances, the casings have been 
 cemented solid with cement from the shoe to the surface. This confines 
 each fluid to its original stratum, assuming the cement sets hard all the 
 way and completely jackets to the casing. 
 
 The advantages of using large quantities of cement are: 
 
 1. When the mud of rotary wells cannot be washed with water, on 
 account of caving formations, the first cement that is pumped out of the 
 shoe scours the mud from the lower formations and casing. This allows
 
 EL, DORADO, ARK., OIL AND GAS FIELD 41 
 
 the final cement to properly bond with them. The first cement will not 
 harden, due to the dilution with mud, but this portion will be on top and 
 its condition will not affect the shut-off. 
 
 2. The cement may seal off water and oil-bearing strata of shallow 
 depth. In the case of rotary wells, it will prevent, as far as it bonds with 
 casing and formation, washing of the absorbed mud and establishment of 
 water infiltration into oil and gas deposits that lie above the shoe. 
 
 3. The casing seat will have additional strength. Large amounts of 
 cement have been used to hold casings that could not be supported by the 
 formation adjacent to the shoe. Also, the possibility of high-pressure oil 
 or gas blowing past the shoe and outside of the casing is lessened. 
 
 4. The casings are protected over a larger surface from corrosive 
 water. The mud fluid of rotary wells is also good protection, provided 
 water does not wash its way to the casing. (See also No. 2.) 
 
 5. The danger of collapsing water strings, due to water pressure, is 
 lessened by reinforcing the casing on the bottom where the greatest pres- 
 sure occurs. When cement is used in this manner, a shallow water de- 
 posit may not exert as high a maximum pressure on the casing as a deeper 
 water, although the two waters would stand at the same level. Suppose, 
 for instance, that a water string is cemented at 2,100 feet and that a good 
 jacket of cement extends to a depth of 1,500 feet. If no water exists in 
 the formations between 1,500 feet and 2,100 feet, the top water cannot exert 
 a pressure at a point lower than 1,500 feet, or no greater than about 700 
 pounds per square inch, for salt water. A thin jacket of cement would 
 suffice to prevent this water from following down the casing and exerting 
 the full hydrostatic pressure on the bottom of the casing. Assume now that 
 a water stratum exists at 1.800 feet and that this water, like the shallow 
 water, would rise to the surface if not obstructed by the cement. It will, 
 therefore, exert a pressure of about 850 pounds per square inch for salt 
 water. When high-head water is sealed with cement alone, it will exert 
 pressure directly on the cement and casing so that thick walls of cement 
 will be necessary to lend substantial reinforcement to the casing. 
 
 The final necessity of thick cement walls will also depend upon the 
 rigidity of the water stratum and upon the amount of cement that hardened 
 in its pore spaces. These considerations, and the possibility of low-head 
 porous strata becoming converted to high-head by secondary water, argue 
 forcibly for thick walls of cement around the lower portions of the casings, 
 especially when the factor of safety against collapse is small. When cement 
 is used in rotary wells, this feature is taken care of usually, as the water 
 strings have a large clearance in most cases. 
 
 6. When the water in the hole is too foul to allow the cement to set, 
 an excess of cement mixed with good water may displace the foul water 
 sufficiently to allow hardening for a certain distance above the shoe . 
 
 The use of large quantities of cement may appear to be a waste, when 
 considering the future recovery of casings in the process of repairs or 
 abandonment. However, a portion of the casing is a small item compared 
 to the total cost of drilling a well, and is very small compared to the pos- 
 sible waste of oil and gas due to water infiltration. These statements, of 
 course, are not strictly true in the case of "wildcat" wells, where under- 
 ground conditions and possibilities have to be learned first. 
 
 Abandonment of Wells: 
 
 It is always expensive and sometimes impossible to re-enter and re 
 pair an improperly abandoned well, and for those reasons it is highly de- 
 sirable to use particular care in the abandonment operations. In this 
 work, each fluid near the oil and gas horizons should be confined, as far 
 as practicable, to its own stratum. If this idea is followed, the recovery 
 of oil and gas from other wells will be increased and, at the same time, 
 valuable deposits of potable water may be protected from contamination 
 by brines or sulphur water. 
 
 A well may be properly drilled and tested, but prove to have no com- 
 mercial production of oil. If such a well is not properly abandoned, how- 
 ever, it may allow water with a high head to travel across the formations 
 to neighboring wells. The improper abandonment of wells in proved areas 
 is usually inexcusable and constitutes a deplorable crime against our 
 natural resources.
 
 42 EL, DORADO, ARK., OIL AND GAS FIELD 
 
 Too much reliance should not be placed on an entire water string left 
 in a well, inasmuch as the rotary-mud protection from corrosion may be 
 overcome by water action after subsistence of the mud, unless the mud 
 was subjected to a considerable closed-in pump pressure. 
 
 The proper use of cement and of mud-laden fluid afford the best means 
 for the proper abandonment of wells. The technique of properly placing 
 cement has been discussed previously. The use of cement for this pur- 
 pose usually calls for a study of the fluid content of the different forma- 
 tions, the probable future worth of present non-commercial deposits and 
 the possible danger of leaving two or more oil strata open together between 
 cement bridges. 
 
 In general, an adequate cement plug should be placed in the bottom of 
 the hole, if necessary, with substantial cement bridges between each pair 
 of water, oil or gas strata. Obviously, the present and possible future con- 
 ditions of the area determine the size and extent of these plugs. The 
 problem would, on first thought, appear to be simplified by cleaning out 
 the well to bottom and filling it with cement to a considerable distance 
 above the oil zone or po'ssible oil zones. Such would be the case, but if 
 the hardness of the cement were not tested at the vital points, efficiency 
 of the work would not be assured. When a well has many showings of oil. 
 with no intervening water, there is a temptation to leave some of the 
 sands open together, with possibly a cement bridge below the bottom 
 showing and one above the top oil deposit. If water appeared in one of 
 these, the other sands might be flooded from a well improperly abandoned. 
 
 In general, long cement plugs and bridges should be set opposite oil 
 sands when a well is abandoned, but they should be tested for hardness 
 at proper depths during their construction. 
 
 The proper method of abandoning wells will vary somewhat according 
 to local conditions. Mud fluid has been used to good advantage in El Dorado 
 for such work. The well should first be cleaned out to bottom, mud 
 pumped through the tubing or extra casing which is then lowered nearly to 
 bottom. The mud should be pumped in until returns of mud have been 
 established at the surface, for several hours. The casing is then packed 
 off and mud forced in under extra pump pressure, using as much heavy mud 
 as possible. t 
 
 Some formations will take enormous quantities of thick mud. It is. 
 therefore, occasionally found expedient to introduce sawdust, chopped rope 
 or straw, etc., into the fluid, in order to assist in clogging the pore spaces. 
 After the lower part of the hole is well mudded, the water strings can be 
 removed and mudding continued up the hole by moving the mudding string 
 upward as the work is accomplished. If there is a conductor string, this 
 can be removed, but the final mudding at the top of the hole should also 
 be done under extra pump pressure in order to seal off the top water. 
 Heavy mud which is free from grit should be used in all of this work. The 
 top of the hole should be protected from debris, and an occasional inspec- 
 tion made to determine whether the mud has receded, in which event more 
 should be added to the top of the column. 
 
 The caving and bridging of formations, as the casings are removed, 
 should be avoided as far as possible, in order to be sure that the mud gets 
 into all porous formations. In this way, each fluid can be kept sealed in 
 its original stratum and a reliable abandonment accomplished. 
 
 Another satisfactory way to abandon a well is to force mud into the 
 formations under considerable pump pressure between cement plugs and 
 bridges. If only the usual pressure due to circulation, or weight of the 
 mud, is used for filling the space between cement bridges, it is possible 
 that a gradual absorption of the fluid by the formation, may occur. This 
 would tend to break the column of mud between the bridges. It might re- 
 sult in a washing of the mud with water and a harmful migration of one 
 or more of the fluids under consideration. It is obvious that this "slack" 
 between bridges cannot be taken up by adding more mud at the surface. 
 A slow movement of mud into the formation may easily appear to be no 
 movement at all. However, as time elapses, a column of mud may un- 
 dergo considerable further absorption. 
 
 The Conservation Commission of Arkansas requires that the producing 
 sands be protected with cement and that the hole then be filled to the sur-
 
 EL DORADO. ARK.. OIL AND GAS FIELD 43 
 
 lace with mud. If the bottom of a well is plugged with cement to a point 
 above the oil sand, and thick mud is then filled in to the surface, the aban- 
 donment would most likely be effective, if more mud could be added in case 
 it receded down the hole. It is, of course, quite possible that a portion of 
 the mud fluid would be held at the surface by the bridging of caved forma- 
 tions, while subsidence took place below that point. The migration of oil, 
 gas or water might then occur below the bridge. In introducing mud into 
 a well, it is also possible to fail to get mud into all parts of the well, on 
 account of bridging formation. It is therefore necessary to mud a well with 
 a string of pipe, starting at bottom and mudding and applying pressure 
 opposite each porous formation which may contaia oil. gas or potable 
 water, as the casing is raised. 
 
 Protection in Case of Deeper Production 
 
 The present producing zone of El Dorado has been definitely assigned 
 by the U. S. Geological Survey, to the Nacatoch subdivision of the Upper- 
 Cretaceous period. It is the history of some neighboring oil fields with 
 Nacatoch production that they have also obtained deeper production and 
 it may be that deeper production will be found at El Dorado. This paper 
 deals with deeper production, only in connection with conservation. With 
 this possibility in mind, adequate means of protecting the various oil de- 
 posits should be considered in case deeper drilling is carried on. 
 
 If a commercial quantity of deeper oil is discovered, there would be 
 general activity toward its exploitation. Either oil wells would be deepened 
 or new wells drilled. For the sake of convenience in discussion, the zones 
 of interest will be designated as follows: Zone A, above a depth of 1,900 
 feet below sea level; Zone B, present productive zone; Zone C, hypothetical 
 deeper production. Zones B and C would be produced from at the same 
 time and through the same or separate wells, depending upon the distance 
 between sands and the character and content of the intermediate forma- 
 tions. Suitable methods for bringing in deeper production are outlined 
 below. 
 
 1. A well can be deepened for lower production (a) by cementing the 
 next smaller casing just above the new production and producing with or 
 without a liner; (b) by recovering all possible of the original water string, 
 side-tracking the remainder and carrying the same size for a deeper shut- 
 off. In (a) enough cement should be used to reach above the shoe of the 
 first water string; in (b) the discarded casing should be plugged with 
 cement before sidetracking in order to prevent its becoming a water chan- 
 nel, mud should be forced into the strata under an extra pump pressure of 
 at least 500 pounds per square inch, and enough cement should be used on 
 the deeper casing to reach at least 300 feet above the top of Zone B. Most 
 of the present water strings are 6-inch and plan (.a) would reduce the hole 
 to 4-inch, or smaller if a liner were used. Such a plan, however, may be 
 found feasible. The general disadvantages of reducing the hole to such 
 small size are, small area of face of hole for oil to drain to, and the ex- 
 cessive danger of sticking tools, bailer or tubing and the difficulty of con- 
 ducting fishing operations in such a small hole. 
 
 Plan (b) may not prove desirable for the reason that it niay be im- 
 possible to reclaim more than 1,200 feet of the water string and that side- 
 tracking with rotary may prove difficult. 
 
 2. New wells could be drilled to obtain lower production. This would 
 involve the question as to the number of strings of casing to use. With a 
 suitable practice already established for production at the present depth, 
 the drilling of new wells for deeper production can be done as follows: (a) 
 cement about 170 feet to 200 feet of 10-inch or 12%-inch casing (as usual), 
 cement second string a short distance above Zone b (as usual), cement 
 third string just above Zone C, using enough cement to reach above the 
 shoe of the next string: (b) omit the second string of (a), put at least 
 500 pounds extra pump pressure on the mud and cement lower string of 
 casing with enough cement to reach at least 300 feet above the top of 
 Zone B.
 
 EL DORADO. ARK., OIL AND GAS FIELD 
 
 By the methods outlined above, adequate protection could be afforded 
 the several oil deposits. The cementing should be carefully done, employ- 
 ing the best practice of the two-plug system. Method (b) has the advantage 
 of saving a string of casing. 
 
 High and low-pressure deposits should not be left open together in the 
 same well on account of probably dissipation of the high-pressure into the 
 low-pressure strata. It is possible that, before abandoning the wells, Zones 
 B and C could be produced simultaneously, by perforating the water string 
 with a long-knife perforator opposite the top of the present production 
 (Zone B). The cement jacket should protect this oil from both top and 
 lower water. If such*was not the case, cement could be forced out through 
 the perforation by means of a bridge, tubing and packing head and produc- 
 tion then resumed from Zone C, or tests made of Zone A. 
 
 Production Record 
 
 Oil Produced, Proven Acreage, Well Spacing: 
 
 As show'n in Table No. 1, the El Dorado field had produced something 
 in excess of 10,000,000 barrels of oil by the end of October, 1921. These 
 production figures are shown graphically in Figure 3 (in pocket). At that 
 date there were about 460 producing wells and an estimated proved acreage 
 of oil and gas territory of 6,825. The average spacing was about fifteen 
 acres per well. 
 
 The figures on proved acreage and spacing are misleading, however, on 
 account of some 2,000 acres of the area being gas bearing to a high degree, 
 thus rendering it undesirable for present exploitation for oil. This leaves 
 about 4,825 acres of territory that may be considered as proved oil terri- 
 tory. Considering the oil area alone, the average spacing of wells at the 
 end of October, 1921, was about 10.3 acres per well (average of 670 feet dis- 
 tance). By the end of November, the average spacing for the entire field 
 had decreased to approximately 8.8 acres per well (619 feet distant). Com- 
 pletions were made at the rate of about eighteen or twenty wells per week 
 during October and November, 1921. 
 
 In the estimate of 4,825 acres of proven oil-producing area, 100 acres 
 were assigned to Section 33-17-15. This may be, as many believe, a sep- 
 arate structure from the main field and its probable further development is 
 necessarily omitted from the accompanying estimates. 
 
 Section 17-18-15 has been drilled more intensively than any other sec- 
 tion in the field. By December 1, 1921, the average spacing in the pro- 
 ductive part of that area was about six acres per well (wells 511 feet apart). 
 There are small tracts in this and other sections of the field where the 
 spacing will approximate three acres per well (362 feet distance). Plate 
 IX gives an idea of the close spacing of wells near the southern boun- 
 dary of Section 17-18-15. 
 
 The general ruling of the State Conservation Commission provides that 
 interior wells shall not be closer together than 400 feet, and that wells 
 shall not be nearer than 200 feet to property lines. In the case of so-called 
 "sh<5e string" properties, the Commission is more lenient, and may con- 
 sider a group of properties as a whole and stagger the wells. An average 
 spacing of 400 feet allows only 3.67 acres per well. In the light of present 
 information, it is safe to say this spacing is undoubtedly too close. 
 
 The following figures, while approximate, are presented to show that, 
 in view of conditions prevailing at El Dorado, an average spacing of seven 
 acres per well is no doubt too close, for this field.
 
 EL DORADO, ARK., OIL AND GAS FIELD
 
 46 EL DORADO. ARK., OIL AND GAS FIELD 
 
 The principal factors to be considered in estimating the proper spacing 
 are: 
 
 (1) Acreage a proven oil area of 4,825 acres has been estimated. 
 
 (2) Cost of Drilling $15,000 is taken as the cost of drilling and equip- 
 ping a well, including its pro-rated general lease expense. This figure is 
 probably too low. 
 
 (3) Total Production From the production data, a production of 
 20,640,000 barrels is assumed for the present proven acreage and reservoir. 
 It is assumed that the wells will not be spaced closer than ten acres per 
 well (average spacing as of October, 1921). Guided by the data of Cutler 
 and Clute* for other fields, it is assumed that: 
 
 9-acre spacing will yield per well 95.0% of yield for 19-acre spacing 
 8-acre spacing will yield per well 89.5% of yield for 10-acr e spacing 
 7-acre spacing will yield per well 84.0% of yield for 10-acre spacing 
 
 (4) Production Cost 35 cents per barrel is assumed as the average 
 cost of production during the productive life of the field. This is meant to 
 include all expenses incurred in production, and includes "overhead" and 
 general charges. This figure is difficult of estimation at this time. 
 
 (5) Lease Prices The figure of $500 per acre for the average price 
 of leases is based on rather meager data, but it will serve for general pur- 
 poses. It is probably low. 
 
 (6) Loss of Oil As indicated by Table I, the loss of oil at El Dorado 
 may be as high as 12 per cent. The figure of 7 per cent is no doubt low. 
 
 (7) Interest A total of 21 per cent is here assumed, regardless of the 
 time of receiving the oil. 
 
 (8) Salvage $1,000 per well is meant to be the average net return 
 from sale and re-use of casing and surface equipment. 
 
 (9) Price of Oil $1.35 per barrel is here assumed. The future price 
 of oil is, of course, a matter of speculation. 
 
 (10) Royalty 12%%, which leaves the selling price of oil to be re- 
 ceived by the lessee as $1.18 per barrel. 
 
 The following estimates (slide rule computation) must be considered 
 as only approximate. They at least prove that an average spacing of as 
 low as four acres per well, is unprofitable. From Plate X (in pocket) it will 
 be seen that wells with an initial average daily production of 480 barrels the 
 first month, will produce during their entire life, an average of 42,800 bar- 
 rels. 
 
 Ten Acres Per Well 
 
 4825 acres-v-10 acres=482 wells 
 
 482 wells @ $15,000 drilling and equipment cost $ 7,230,000 
 
 482 wells @ 42,800 bbls. each, 20,640,000 bbls. @ 35c production- 
 cost 7,225,000 
 
 4825 acres @ $500 for leases 2,412,000 
 
 Loss of oil (7%) 1,445,000 bbls. @ $1.18 1.706,000 
 
 Interest, 21% of investment , 3,900,000 
 
 $22,473,000 
 
 Oil sold, 19,195,000 bbls. @ $1.18 $22,640,000 
 
 Salvage of casing and surface equipment, $1,000 per well 482,000 
 
 $23,122,000- 
 22,473,000 
 
 Cain $649.000 
 
 *Cutler, W. W., and Clute. Walker S., Relation of Drilling Campaign to 
 Income -from Oil Properties Reports of 1ni'csti(jations. U. S. Bureau of Mines, 
 August, 19*1.
 
 EL DORADO, ARK., OIL AND GAS FIELD 47 
 
 Nine Acres Per Well. 
 
 4825 acres-^-9 acres 536 wells 
 
 536 wells @ $15,000 drilling and equipment cost $ 8,040,000 
 
 536 wells @ 40,600 bbls. each, 21,800,000 bbls. @ 35c production 
 
 cost '. 7,640,000 
 
 4825 acres @ $500 for leases 2,412,000 
 
 Loss of oil (7%) 1,525,000 bbls. @ $1.18 1,800,000 
 
 Interest, 21% of investment 4,175,000 
 
 $24,067,000 
 
 Oil sold, 20,275,000 bbls. & $1.18 .- $23,920,000 
 
 Salvage of casing and surface equipment. $1,000 per well 536,000 
 
 $24,456,000 
 24,067,000 
 
 Gain $389.000 
 
 Eight Acres Per Wei!. 
 
 4825 acres-^8 acres=603 wells 
 
 603 wells @ $15,000 drilling and equipment cost $ 9,045,000 
 
 603 wells @ 38,300 bbls. each, 23,100,000 bbls. @ 35c production 
 
 cost 8,090,000 
 
 4825 acres @ $500 for leases 2,412,000 
 
 Loss of oil (7%) 1.616,000 bbls. @ $1.18 1,907,000 
 
 Interest, roughly 21% 4,510,000 
 
 $25,964,000 
 
 Oil sold, 21,484,000 bbls, @ $1.18 $25,380,000 
 
 Salvage of casing and surface equipment, $1.000 per well 603,000 
 
 $25,983,000 
 25,964,000 
 
 Gain $19,000 
 
 . : Seven Acres Per Well 
 
 4825 acres^-7 acres=689 wells 
 
 689 wells @ $15,000 drilling and equipment cost $10,335,000 
 
 689 wells @ 35,960 bbls., 24,790.000 bbls, @ 35c production cost.... 8,675,000 
 
 4825 acres @ $500 for leases 2,412,000 
 
 Loss of oil (7%) 1,734,000 bbls. @ $1.18 2,046,000 
 
 Interest about 21% 4,933,000 
 
 $28,401,000 
 
 Oil sold. 23,056,000 bbls., @ $1.18 - ...$27,220,000 
 
 Salvage of casing and surface equipment, $1,000 per 
 
 well 689,000 27,909,000 
 
 Loss $ 492,000 
 
 It may be interesting to note that approximately 22,400,000 barrels of 
 oil would be produced with the following factors: 
 
 (1) A proven acreage of 4,825. This does not mean that extensions 
 to the field will not be made. 
 
 (2) An average thickness of twelve feet for the saturated portion of 
 the reservoir formation. The data is rather meager on this point. 
 
 (3) An average porosity of 25 per cent. On account of the inco- 
 herence of the sand, 'no samples have been obtained on which porosity tests 
 could be made. In an uncemented sand, the porosity may be rather high. 
 
 (4) An ultimate recovery of 20 per cent of the total oil underground 
 Either of the last three factors or the production from the 4,825 acres. 
 
 may have a different value, in which case one or more of the other factors 
 would be affected.
 
 48 EL DORADO, ARK., OIL AND GAS FIELD 
 
 Several factors that will influence the spacing of wells, are: Possible 
 profits that can be derived, estimated amount of oil recoverable with differ- 
 ent spacings, porosity and size of grain of reservoir formation, gravity of 
 oil, gas pressure and depth. The relation of well spacing to possible profits 
 derivable from production, is one of the most important factors and has 
 not, in general, received much attention. . It is apparent that a larger ulti- 
 mate net profit expected on operations will justify a larger expenditure by 
 drilling more wells, in order to extract more oil in a shorter period, thereby 
 decreasing the total interest charges on the money invested. Expected 
 profits can easily be swallowed up when close-spacing is used, by excessive 
 total cost and attendant interest, depreciation and amortization charges. 
 
 The individual productions of wells vary considerably at El Dorado. 
 The records show that numerous wells have increased their production tem- 
 porarily at different points during the general decline of production. This 
 condition is, no doubt, due primarily to sand trouble. After a well frees 
 itself of sand or is cleaned out, the production usually increases. The ac- 
 cumulation of sand and waxy sediment in the liner or screen, or the lower 
 portions of the tubing, may seriously retard production. 
 
 Like most oil fields, El Dorado has some so-called "spotted" territory. 
 For example, a well of 2,200 barrels initial flow was located in the midst 
 of small producers. Its decline was abnormally rapid, however. The rock 
 pressure is said to have been low and not well sustained, and it was ap- 
 parently an isolated prolific spot. 
 
 Quality of Oil: 
 
 Some of the oil runs as high as 37.5 degrees Baume gravity. It averages 
 about 35.5 degrees Baume gravity and is placed in the class of paraffin 
 base oils. Analyses from various parts of the field indicate that the crude 
 averages about 31 per cent gasoline and 15 per cent distillate. The sul- 
 phur content is rather large, frequently exceeding one per cent. 
 
 Surface Wastage: 
 
 In developing an oil field, it is impossible to avoid all waste, especially 
 during the pioneer period. It is possible, however, to curtail waste to a 
 greater extent than is usually done. There is much oil lost, due to the 
 rush in completing wells that could be prevented with little extra time and 
 expense. 
 
 Evaporation losses are field losses that will probably never be en- 
 tirely eliminated, but remarkable economy can be effected. Wiggins* has 
 shown by numerous experiments and data that the average evaporation 
 loss for the Mid-Continent fields is 6.2 per cent, divided among the va- 
 rious operations as follows: 
 
 APPORTIONMENT OF THE EVAPORATION LOSS SUSTAINED BY 
 
 CRUDE OIL ON ITS JOURNEY FROM THE WELL 
 
 TO THE REFINERY 
 
 Per Cent Volume Evaporated Source of Information 
 
 Location of Loss Summer Spring Winter Avg. 
 
 Plow tank 
 
 1.2 
 
 1.0 
 
 0.8 
 
 1.0 
 
 Estimate plus test on 
 
 
 
 
 
 
 filling lease tank 
 
 Tilling lease tank 
 
 . 1.2 
 
 1.0 
 
 0.8 
 
 1.0 
 
 Test 
 
 Lease storage 
 
 1.8 
 
 1.4 
 
 1.2 
 
 1.5 
 
 Test 
 
 Gathering 
 
 1.3 
 
 0.9 
 
 0.8 
 
 1.0 
 
 Test 
 
 Transportation .. 
 
 1.2 
 
 0.9 
 
 0.8 
 
 1.0 
 
 Estimate plus tank 
 
 
 
 
 
 
 tests 
 
 
 
 
 
 
 Test on filling large 
 
 
 
 
 
 
 tank 
 
 Tank farm 
 
 0.9 
 
 0.7 
 
 0.6 
 
 0.7 
 
 Test 
 
 Total 
 
 7.6 
 
 5.9 
 
 4.9 
 
 6.2 
 
 (By addition) 
 
 
 
 
 
 
 
 
 
 
 
 
 
 *Wiggins, J. H., Evaporation Losses of Crude Oil in Storage in the Mid- 
 Continent. Bulletin No. 200, Bureau of Mines (in press). Advance chapters in 
 trade journals.
 
 EL DORADO, ARK., OIL AND GAS FIELD 
 
 4!) 
 
 The conclusion as drawn by him is: "This figure of 6.2 per cent when 
 applied to the 196,000,000 barrels produced in the Mid-Continent fields 
 shows that 12,152,000 barrels is the yearly evaporation bill. In gallons, it 
 equals 510,000,000, which is just about the total gasoline produced by the 
 natural gas-gasoline industry in the United States in 1919." 
 
 Gasoline, the most valuable portion of the crude, sustains the entire 
 loss, and the money value lost is much higher than the 6.2 per cent volume 
 loss. Wiggins has proved that air contact with, and movement over, the 
 'surface of the oil, is responsible for the large evaporation losses. If 
 storage tanks have covers actually tight and arrangement is made to relieve 
 pressure through a liquid seal, evaporation will be greatly reduced. After 
 a tank has been provided with a tight cover, an efficient combination safety 
 valve and air excluder can be made by connecting one or more goose-neck 
 pipes to the cover in such a manner that about four inches of oil or 
 water can stand in the bend. Such protection will pay for itself in a short 
 time, even though the producers' loss is in volume only. If an oil is of 
 sufficiently high gravity to remain in the top price division after loss by 
 evaporation, the producer actually loses only in proportion to the volume. 
 The refiner's losses are in gasoline. 
 
 One operator at El Dorado reports that 7,000 barrels of oil stored in 
 a tank with a steel top lost 4 degrees Baume gravity in six months. The 
 gravity was decreased from 36 to 32 degrees. The loss in barrels of oil 
 was not ascertained. 
 
 Table 5 
 
 Table 5 gives an analysis of typical El Dorado crude oil, made in the 
 Pittsburgh laboratory of the Bureau of Mines: 
 
 Specific gravity, 0.852 
 
 Per cent sulphur, 0.83 
 
 Saybolt Univeral viscosity at 70 F. 57.0 
 
 Saybolt Universal viscosity at 100 F. 46.6 
 
 Baume gravity, 34.30 
 
 Per cent water, 0.1 
 
 Pour test, below 5 1 F. 
 
 Distillation, Bureau of Mines Hempel Method 
 
 Air distillation, Barometer 749 
 
 mm. 
 
 First drop, 31 C. (88^ F.) 
 
 
 Per 
 
 Sum 
 
 
 Cloud 
 
 
 Temperature 
 
 cent 
 
 per 
 
 Sp. Gr. 
 
 B test 
 
 Temperature 
 
 C 
 
 cut 
 
 cent 
 
 cut 
 
 cut Viscosity P. 
 
 i?' 
 
 Up to 50 
 
 
 
 
 
 Up to 122 
 
 50 to 75 
 
 4.5 
 
 4.5 
 
 0.680 
 
 75.9 
 
 122 to 167 
 
 75 to 100 
 
 4.2 
 
 8.7 
 
 .701 
 
 69.7 
 
 167 to 212 
 
 100 to 125 
 
 7.1 
 
 15.8 
 
 .722 
 
 63.9 
 
 212 to 257 
 
 125 to 150 
 
 6.2 
 
 22.0 
 
 .746 
 
 57.7 
 
 257 to 302 
 
 l&O to 175 
 
 5.1 
 
 27.1 
 
 .772- 
 
 51.3 
 
 302 to 347 
 
 175 to 200 
 
 3.6 
 
 30.7 
 
 .795 
 
 46.1 
 
 347 to 392 
 
 200 to 225 
 
 3.5 
 
 34.2 
 
 .810 
 
 42.8 
 
 392 to 437 
 
 225 to 250 
 
 4.4 
 
 38.6 
 
 .823 
 
 40.1 
 
 437 to 482 
 
 250 to 275 
 
 5.1 
 
 43.7 
 
 .833 
 
 38.1 
 
 482 to 527 
 
 Vacuum distillation at 40 mm. 
 
 Up to 200 
 200 to 225 
 225 to 250 
 250 to 275 
 275 to 300 
 
 5.5 
 
 6.5 
 
 5.4 
 4.6 
 
 5.5 
 12.0 
 17.9 
 23.3 
 
 27.9 
 
 .853 
 .860 
 .874 
 .890 
 .903 
 
 34.1 
 32.8 
 30.2 
 27.3 
 25.0 
 
 40 
 45 
 
 60 
 
 81 
 
 132 
 
 Up to 392 
 392 to 437 
 437 to 482 
 482 to 527 
 527 to 572 
 
 Carbon residue of residuum 10.3%. 
 
 Approximate Summary 
 
 Gasoline and naphtha 
 Kerosene ... 
 
 Gas oil 
 
 Light lubricating disfliat 
 Medium lubricating distillate 
 
 Per 
 
 cent. 
 307 
 
 Sp. 
 Gr. 
 0.735 
 
 B. 
 
 60.5 
 
 13 
 
 .823 
 
 40 1 
 
 12.0 
 ;e 11.3 
 late :. 4.6 
 
 .857 
 .882 
 .903 
 
 33^4 
 
 28.7 
 25.0
 
 50 EL DORADO, ARK., OIL AND GAS FIELD 
 
 The senior author developed a formula in 1916, for use in estimating 
 mixtures of light and heavy oils to make up tank car shipments of a cer- 
 tain desired gravity and to use a minimum of light oil in the mixture. 
 This formula was developed mathematically and assumes that there is no 
 volume shrinkage after two oils are mixed. 
 
 It is interesting to note that the results from the use of this formula 
 give results of oil lost by evaporation which check closely with an estimate 
 of J. H. Wiggins, of the volume lost in the case cited above. Mr. Wiggins 
 has been working for two years on evaporation losses of Mid-Continent 
 crudes. The formula is as follows: 
 
 Ax (Ba Bx) (Bs+130) 
 
 (Bx Bs) (Ba+130) + (Ba Bx) (Bs+130) 
 
 Where "A" is amount of oil, "B" is Baume gravity of oil, "a"' refers to por- 
 tion added, "s" refers to portion at start and "x" refers to the mixture. In 
 solving the problem given above, it can be assumed that 70 degree gasoline 
 was added to the remaining 32 gravity oil to make up 7,000 barrels 
 of 36 gravity oil. Assume that the average gravity of the evaporated por- 
 tion was 70 degrees (corresponds to oil analyses). Then Ax=7,000, Ba=70. 
 Bs=32, Bx=36. Substituting in the formula. 
 7000X34X162 
 
 As =6112 barrels. 
 
 (4X200) + (34X162) 
 
 which was the amount of oil remaining after evaporation. The amount 
 evaporated was then 888 barrels, or 12.7 per cent. The efficiency of this 
 cover in excluding air circulation is not known and the same is true of the 
 determination of the loss of gravity. A small additional expenditure in 
 proper design of the tank cover would have reduced the evaporation losses 
 greatly. 
 
 Besides evaporation, there has been a great deal of oil lost at El Dorado 
 by spray, poor separation from water, inadequate storage for uncontrolled 
 wells, seepage and fire. Plate XI shows a rapidly constructed sump for an 
 uncontrolled well. A great deal of oil ran along the natural surface drain- 
 
 Plate XI. Waste of Oil by Storage in Earthen Sump. 
 
 age channels, where much of it was lost by evaporation, seepage and fire. 
 Some of it has been reclaimed by the operating companies and by in- 
 dividuals. The oil thus reclaimed by impounding and skimming has usually 
 lost most of its gasoline. Because of the recent increase in the price of 
 crude oil, operators will, no doubt, exert more effort toward conservation 
 of their oil
 
 EL DORADO, ARK., OIL AND GAS FIELD 51 
 
 As a protection against the spread of fire, all steel-storage tanks 
 should each be surrounded by earthen walls of suitable height and distance 
 from the tank. Bowie* gives detailed information on this subect. A por- 
 
 Plate XII. A 55,000-Barrel Steel Tank on the Standard Oil Tank Farm. 
 Shows Portion of Adequate Fire Wall which Centers the Tank in a Closed 
 Basin. 
 
 tion of a 55,000-barrel steel tank with a suitable tire wall is shown in Plate 
 XII. It is located on the Standard Oil tank farm at El Dorado. Such tanks 
 should also be protected by a complete fire foam equipment. 
 
 The waste of gas at the surface has not been unusually large. The 
 principal losses have occurred from blowing wild. In certain areas, the 
 gas waste may be sufficient to reduce the total recovery of oil by ordinary 
 methods. If gas is allowed to escape in large quantities, it by-passes oil 
 in the sand and cuts down the ultimate recovery. This is due to the gas 
 being much more fluid than the oil and it, therefore, encounters less re 
 sistance to passage through the reservoir. The sand then becomes too rap- 
 idly impoverished of gas and the oil recovery is diminished. 
 
 For other oil fields, production statistics and physical measurements 
 of underground factors, such as sand thickness and porosity, indicate that 
 there is always more oil left underground that is raised to the surface. Es- 
 timates of the total recovery of oil by ordinary means, vary from 10 per 
 cent to 40 per cent of total oil underground. With this in mind, it is not 
 difficult to realize how necessary it is to consider every possible means 
 of aiding recovery. A few additional per cent of ultimate extraction may 
 represent millions of barrels of oil. 
 Production of Gas: 
 
 As pointed out previously, there are about 2,000 acres of proved gas 
 producing area in the El Dorado field. This area is being developed Only 
 enough to supply the local needs for gas. As the gas is depleted from the 
 oil deposits of the same strata, tiiere will no doubt be some transfer of gas 
 to them from the gas area. The conservation of gas is urged, therefore, 
 as it may assist in the recovery of the oil in adjacent areas. 
 
 An estimation of the total amount of gas used and wasted is not at- 
 tempted on account of incomplete information. 
 
 Up to about September 10, 1921. 
 At least 50 wells had been completed with an initial open flow in excess of 
 
 5,000,000 cubic feet of gas per day; 
 At least 33 wells had been completed with an initial open flow in excess of 
 
 10,000,000 cubic feet of gas per day; 
 
 * Bowie, C. P., Oil Storage Tanks and Reservoirs, Bulletin Xo. 7-55. U, S. 
 Bureau of Alines. 1918. Extinguishing and Preventing Oil and Gas I- ires, Bulle- 
 tin No, 179. U. S. Bureau of .^fincs. IQ^O.
 
 52 
 
 EL DORADO. ARK., OIL AND GAS FIELD 
 
 At least 24 wells had been completed with an initial open flow in excess of 
 15,000,000 cubic feet of gas per day; 
 
 At least 12 wells had been completed with an initial open flow in excess of 
 
 20,000,000 cubic feet of gas per day; 
 And 5 wells had been completed with an initial open flow in excess of 
 
 25,000,000 cubic feet of gas per day. 
 
 These statistics, together with Table 6, will give some idea of the amount 
 of gas that has been available. 
 
 Some of the wells show very rapid decline of gas production and pres- 
 sure. Water infiltration has, in many cases, undoubtedly been a factor in 
 shortening the life of these wells. 
 
 Table 6 
 
 DECLINE IN GAS PRESSURE AND PRODUCTION OF SOME OF THE WELLS 
 
 OF EL DORADO 
 
 1 921 
 
 WELL 
 
 Section 
 
 * Completed 
 
 V 
 
 Rock Pressure Working Open Flow Capacity 
 Lbs. per Sq. In. , Pressure Thousands of Cubic Ft. 
 
 "oj 
 j3 
 
 
 
 bi 
 
 3 
 < 
 
 CO 
 
 +j 
 a 
 a> 
 m 
 
 
 rH 
 
 G 
 <D 
 
 m 
 
 c- 
 
 N 
 
 ti 
 3 
 
 < 
 
 jo 
 
 "G 
 o> 
 rf) 
 
 ^ 
 
 I 
 
 "3 
 
 's 
 
 
 
 ci 
 
 CO 
 
 CD 
 
 rn 
 
 o 
 
 P. 
 
 Cv 
 
 00 
 
 McCauldin 1 (?) 
 Lacy No 1 
 
 31-17-15 
 
 31-17-15 
 6-18-15 
 6-18-15 
 36-17-16 
 26-17-16 
 31-17-15 
 6-18-15 
 1-18-16 
 |12-18-16 
 
 6-'21 
 5-12-'21 
 2- 8-'21 
 8-ll-'21 
 
 2-20-'21 
 4-'20 
 
 700 
 960 
 
 720 
 
 600 
 
 900 
 960 
 
 140 
 115 
 140 
 140 
 150 
 480 
 120 
 110 
 Ki 
 
 120 
 115 
 140 
 140 
 150 
 320 
 120 
 110 
 led 
 
 
 no 
 
 115 
 120 
 120 
 150 
 315 
 110 
 110 
 
 by 
 
 100 
 100 
 100 
 100 
 115 
 300 
 90 
 90 
 salt 
 
 90 
 85 
 85 
 70 
 115 
 190 
 80 
 90 
 wa 
 
 90 
 
 85 
 70 
 70 
 115 
 190 
 70 
 90 
 ter 
 
 35,000 
 35,000 
 25,000 
 15,000 
 
 13,000 
 25,000 
 
 31,000 
 30,000 
 
 18, 000| 15,000 13,500 
 16,000|13, 000(13,000 
 15,000 1 10,000 1 6,000 
 10,000 1 6,000 1 5,000 
 2,500 2,500 1 1,500 
 11,000 1 11,000 110,00'0 
 15,000 1 15, 000| 13,000 
 6,000| 6,000 1 6,000 
 Dead 
 Dead 
 
 Chal Daniels 
 Woodly et al., 1 
 Miles No. 1 
 Heartstone 
 Burns No 1 
 
 Reynolds 
 "Home" Well 
 Constantin 
 
 The active gas wells listed above are blown daily, tri-weekly or weekly 
 for ten or fifteen minutes, for the purpose of freeing them of water. This 
 procedure has probably drilled some of the wells, in the unconsolidated 
 sand, deeper, which may increase the inflow of water. As the gas occurs 
 on the higher portions of the structure, edge-water could hardly be ex- 
 pected to appear there during the early life of the field. The blowing of 
 gas wells to full capacity is a practice that should be reduced to the min- 
 imum whenever possible. If water is not already present in some cases, 
 this will aid in drawing it in rapidly. When wells are producing gas with 
 a large quantity of water, the well should be repaired or at least plugged 
 high enough to retard the inflow of water, if it is coming through the gas 
 sand. 
 
 Besides blowing wells to free them of accumulated water, they are 
 also blown "open" to ascertain their mechanical condition, to clean out the 
 pore spaces of the formation, to allow the wells to be repaired, and to make 
 open-flow tests. Water can be removed from gas wells by a gas syphon 
 line, which does not interrupt the gas service of the well. There is some 
 loss of gas incurred when a syphon line is used, but the amount required to 
 lift the water to the surface is relatively small. The frequency of open 
 flow tests can well be deduced by a study of the data of pressure readings 
 and calculation of capacities therefrom. When a well must be blown, it 
 should be done by an experienced man who is familiar with the physical 
 condition of that well.
 
 EL DORADO, ARK., OIL AND GAS FIELD 
 
 The National Committee on Natural Gas Conservation adopted the fol- 
 lowing resolution on June 11, 1920: 
 
 "Resolved, That the practice of 'blowing heads' off wells for 
 long periods to get open-flow tests at stated intervals be discon- 
 tinued. That pressure tests by closing 'side gates' or the use of 
 other practical measuring schemes be used. That wells should 
 only be 'blowed' when practical men know it to be necessary." 
 
 El Dorado natural gas is at present used for power, lighting and heat- 
 ing in the field, by the local refineries and industries and by the city of 
 El Dorado. The El Dorado Natural Gas Company distributes most of the 
 gas and reports an average daily consumption of about 19,500,000 cubic feet. 
 The wells are drawn on to about 20 per cent of their capacity. 
 
 Some tests made by operating companies show that the gravity of the 
 casinghead gas varies from .74 to .92 and the dry gas runs about .60. Re- 
 liable data on gasoline content of the gas were not obtained. 
 
 Production Decline Curves for Oil Wells: 
 
 The production records of practically every well in the El Dorado field 
 were obtained and used in making the production decline and future pro- 
 duction curves. The production records of certain individual wells were 
 available, but in general the average production per well of each group 
 was used. On most producing properties, the oil from several wells is 
 run into the same tank. Because the correct water content may not have 
 been deducted in every case and the date each well started to produce was 
 not always available, there may be some inaccuracies in certain of the rec- 
 ords. However, it is likely that these inaccuracies are compensating. Some 
 records .of groups of wells were rejected on account of being too greatly- 
 affected by the unknown flush production of new wells. 
 
 The production figures of each well, or average of a group, were tabu- 
 lated in terms of average barrels per day by months. These data, as shown 
 in Table 7, include October, 1921. In arranging these figures, the "mathe- 
 matical method" described on page 88 of the 1921 Manual for the Oil and 
 
 Table 7 
 
 Estimated Future and Ultimate Production for an Average Well in the 
 El Dorado Field. 
 
 Estimated 
 
 Remaining 
 
 Life 
 
 Well 
 Months 
 
 23 
 
 22 
 21 
 20 
 19 
 18 
 17 
 16 
 15 
 14 
 13 
 12 
 11 
 10 
 
 ii 
 
 Est. Average 
 
 Daily Prod. 
 
 Per Well 
 
 Per Month 
 
 Barrels 
 
 10,000 
 
 4,600 
 
 2.300 
 
 1,250 
 
 700 
 
 420 
 
 255 
 
 165 
 
 106 
 
 74 
 
 52 
 
 37 
 
 26 
 
 19 
 
 14.5 
 
 11 
 
 8.5 
 
 6.5 
 
 5 
 
 4 
 
 3.2 
 2.6 
 
 in 
 
 Estimated 
 
 Monthly' 
 
 Production 
 
 Ool. 11x30.4 
 
 Barrels 
 
 304,000 
 
 139,840 
 
 69,920 
 
 38,000 
 
 21,280 
 
 12,768 
 
 7,752 
 
 5,016 
 
 3,222 
 
 2,250 
 
 1,581 
 
 1.125 
 
 790 
 
 578 
 
 441 
 
 334 
 
 258 
 
 198 
 
 152 
 
 122 
 
 97 
 
 79 
 
 61 
 
 IV 
 
 Est. Future 
 Production 
 of Average 
 
 Well 
 Barrels 
 
 305,864 
 
 166,024 
 
 96,104 
 
 58,104 
 
 36,824 
 
 24,056 
 
 16,304 
 
 11,288 
 
 8,065 
 
 5,816 
 
 4,235 
 
 3,110 
 
 2,320 
 
 1,742 
 
 1,301 
 
 967 
 
 708 
 
 511 
 
 359 
 
 237 
 
 140 
 
 61 
 
 
 
 V 
 
 Est. Total 
 
 Ultimate Prod. 
 
 of Average Wei 
 
 Col. III + IV 
 
 Barrels 
 
 609,864 
 
 ;?05,864 
 
 166,024 
 
 96,104 
 
 58,104 
 
 36,824 
 
 24,056 
 
 16,304 
 
 11,287 
 
 8,066 
 
 5,816 
 
 4,235 
 
 3,110 
 
 2,320 
 
 1,742 
 
 1,301 
 
 966 
 
 709 
 
 511 
 
 359 
 
 237 
 
 140 
 
 61
 
 54 EL DORADO. ARK., OIL AND GAS FIELD 
 
 Gas Industry (issued by the Treasury Department) was used. W. W. Cut- 
 ler, petroleum engineer of the Bureau of Mines, co-operated in the work ot 
 preparing production figures for El Dorado. 
 
 The first month's production of each well or group was tabulated in 
 the column whose average approximated that production, and subsequent 
 monthly productions were placed in successive columns. The averages of 
 the columns were then taken as the basis for the average production de- 
 cline curve shown in Plate XIII. In this way, the old wells of small initial 
 production served to extend the curve some months in the future. This 
 method is used in accordance with the law of Beal and Lewis (Bureau of 
 Mines), which states that when wells are producing under similar condi- 
 tions and have the same present rate of production, they will, on the av- 
 erage, decline at the same rate, regardless of their relative ages. In ex- 
 tending the average future production to the assumed economic limit of 
 two barrels per day, logarithmic cross-section paper was used. The curve 
 was straightened and projected in the manner described in the Treasury 
 Manual. 
 
 When wells came in as strong gassers and made very little oil at first, 
 the month of maximum oil production was assumed as the first month. 
 There were not many cases of this character. 
 
 After the field began producing, it was soon evident that the use of 
 "chokes" was advisable and their use became general. The effect of 
 "chokes" on production has been, of course, to make the decline more 
 gradual. This is accomplished by holding back the oil and gas from a 
 rapid discharge and this, in turn, delays a water-coning effect in the sand. 
 The average decline curve is, therefore, somewhat modified by this factor 
 during the flush production period. 
 
 The production decline curve here presented was constructed mainly 
 from the records of flowing wells. It may be that when pumping becomes 
 the common method of operation throughout the field, the production de- 
 cline curve will be more sustained. 
 
 After preparing the average production decline curve, the records were 
 divided into groups: (1) those of wells whose first month's productions 
 were greater than 500 barrels per day, and (2) those of wells whose first 
 month's productions were greater than 500 barrels per day. This showed 
 that both large and small wells conformed in decline with the average pro- 
 duction decline curve. Decline curves for the northern and southern parts 
 of the field were also constructed, but were so near alike that they are 
 omitted and only the average curve is shown in Plate XIII. 
 
 Table No. 7 is based on the average production decline curve shown 
 in Plate XIII. Column II shows the estimated average daily production 
 per well per month. The figures were obtained from the ordinates of the 
 average decline curve (Plate XIII) at the points representing the various 
 months. For any particular case, these figures can be considered as first 
 month's production or as the production of any other month. Column III 
 represents the corresponding total monthly production, the figure 30.4 being 
 used as the average number of days in a month. Column IV shows the 
 sum of the monthly production subsequent to that shown in Column III, if 
 the average well is produced down to an assumed economic minimum ot 
 two barrels per day. 
 
 Column V is the sum of columns III and IV and represents the sum ol 
 the present month's total production and the estimated future production, 
 of an average well. 
 
 It is likely that the economic limit of commercial production will be 
 somewhat higher than for most oil fields on account of the large quantities 
 of water that will" probably have to be lifted with the oil. Sand trouble is 
 also a factor that may cause an earlier abandonment. At present, many of
 
 EL DORADO, ARK., OIL AND GAS FIELD 
 
 the small producing wells are off production a large part of the time on 
 account of sand troubles. One probable compensating feature of the con- 
 tinuous sand movement is the elimination of deposits of paraffin and other 
 clOb'ging material on the walls of the hole. 
 
 It must not be inferred from Table 7 that the field will produce com- 
 mercially no longer than twenty-three months. The average well with a 
 first month's production of 10,000 barrels, for instance, will produce for 
 twenty-three months to an economic limit of two barrels per day, or will 
 produce for twenty-three months longer after it has declined to an average 
 monthly production of 10,000 barrels per day. New wells may be drilled 
 after the first producers are abandoned and the actual life of the field 
 would thus be extended. The curves and table apply to the present pro- 
 ducing oil zone only. 
 
 The curves of Plate X were prepared from the data of Table No. 7 and 
 are for the purpose of interpolation as well as graphic representation. 
 
 Production Methods 
 
 When drilling in high-pressure gas areas, such as the El Dorado field, 
 it is essential that the control equipment at the surface be of sufficient 
 strength to be safe. In this field, special valves and fittings must be used, 
 as there is considerable sand produced with the oil and the wear is exces- 
 sive. Plate XIV shows a steel choke badly worn by sand. 
 
 Plate XIV. A Steel Choke Worn by the 
 Passage of Sand with Oil.
 
 56 
 
 EL DORADO. ARK.. OIL AND GAS FIELD 
 
 Safety Devices: 
 
 The usual casinghead fittings which are commonly used in the El Do 
 rado field (see Plate XV) are made up as follows: 
 
 Plate XV. "Christmas Tree" Equipment of About Average Design. 
 
 (1) Master Valve A heavy gate valve attached to the 6-inch water 
 string, preferably placed below the derrick floor and operated by an exten- 
 sion arm in case of emergency, such as fire or blow-out. In order to ob-
 
 EL DORADO, ARK., OIL AND GAS FIELD 
 
 57
 
 58 EL DORADO. ARK., OIL AND GAS FIELD 
 
 viate the danger of the master gate being blown off of the 6-inch pipe, 
 clamps and tie rods are used as shown in Plate XV and Figure 4. The 
 lower clamp is placed below a collar and around the 10-inch conductor pipe. 
 These clamps consist of two iron bars with dimensions of about one inch 
 by six inches by four feet, bolted together around the casing and connected 
 by tie rods. The end threads allow proper adjustment and distribution of 
 the strain due to pressure. 
 
 (2) Control Head When the well is finished with cable tools, the 
 drilling should be done through the master valve and the control head. In 
 case gas becomes bothersome before the tools are removed, the control 
 head can be closed on the line and a reasonably tight seal effected. A tee 
 placed between the master valve and control head should be connectd up 
 and in readiness for delivering oil and gas or lor mudding the well and 
 killing the flow, should that become necessary. When the wells are being 
 finished with rotary tools, it is well to have packing clamps or a blow- 
 out preventer in readiness for emergency when removing the drill stem. By 
 using such devices and paying proper attention to the thickness and height 
 of the mud fluid, wild wells should not occur, except in cases of accident. 
 
 (3) "Christmas Tree" Above the master valve is placed a cross 
 from which lead the flow lines as shown in rtate XV. These lines are pro- 
 vided with gate valves. A nipple and another gate valve is installed above 
 the cross. 
 
 Chokes are sometimes placed at this point, but they are, in general, 
 needed only on the separator. The chokes are cylindrical steel blocks, 
 threaded on each end, with their length about twice their diameter and 
 having a small hole longitudinally through their center. Substantial gate 
 valves are placed on each flow line for the purpose of shifting, regulating 
 or stopping the flow. 
 
 The valves and fittings used in El Dorado should be of a heavy type, 
 with sufficient margin of safety over the field pressure, in order to allow 
 for wear and abrasion by the sand. In some of the worst sand producing 
 wells, the valves, chokes and fittings are rapidly worn out, unless the flow 
 is properly controlled. For instance, on one well, a 6-inch valve seat was 
 ruined in half an hour. Fittings to withstand pressures of 2,509 pounds 
 per square inches are now commonly used. 
 
 Oil, Gas and Water Separators: 
 
 The oil-gas-water separators in common use at El Dorado, consist of 
 about seven joints of 10-inch pipe with oil and gas risers at each end. Fig- 
 ure 4 shows the type of separator generally used at El Dorado. The oil 
 riser at the higher end of the separator consists usually of two 4-inch ver- 
 tical nipples about 6 feet in height, each having at the top a 4-way tee 
 connected to chokes of sizes from % to 1 inch. The number and size of 
 chokes used will depend on conditions. Another nipple extends from a 
 central tee and connects with the flow line to storage. The chokes are 
 required for high-presure wells, in order to lessen the flow and thus reduce 
 water and sand trouble. The decrease in flow by the use of chokes tends 
 to prevent the formation of "cut oil." A more complete separation of gas 
 and oil is accomplished in the last (high) risers. The separator is gen- 
 erally inclined, being about six feet higher at the end farther from the 
 well, in order that the water may separate readily at the lower end. 
 
 For the purpose of bleeding off water and sand, three or four lateral 
 6-inch lines of three joints each are connected on the under side and near 
 the lower end of the 10-inch pipe by means of tees or welded connections. 
 The opposite ends are swedged down, so that 2-inch gate valves can be 
 used for regulating the flow of water. The bleeders are regulated so that 
 each will carry about an equal distribution of water, in order to avoid ex- 
 cessive suction action on- the oil in the separator at any particular point. 
 
 Plates XVI and XVII show the water being discharged from sepa- 
 rators. 
 
 Some of the operators believe that emulsion forms after a mixture of 
 oil and water passes through the chokers, due to the expansion of gas. If 
 this is true, it is desirable to have a sufficient number of bleeders to draw 
 off as much free water as possible and prevent any water from reaching 
 the chokers at the end of the separator. It is never possible to sep-
 
 EL DORADO, ARK.. OIL AND GAS FIELD 
 
 59 
 
 arate all the water, but some of the oil is freed of water in this way and 
 the amount of emulsion which can form is thus cut down. In the event 
 of emulsions forming before the oil reaches the surface, the separators 
 will not cut down that which had already been formed, but may assist in 
 preventing the formation of additional emulsions. The exclusion of water 
 is the only certain means of preventing the formation of emulsion, although 
 
 
 Plate XVI. Discharge of Water and Some Oil from Separator. Gas 
 and Oil Risers at Ends of Separator not shown. Some Oil being Wasted 
 with the Water through the Bleeders. 
 
 Plate XVII. Discharge of Water from Separator, Clear Water being 
 Discharged from the Bleeders. 
 
 when the gas pressure is reduced, gas expansion will not be so serious a 
 factor in forming emulsified oil. The large quantities of gas acompanying 
 oil in the El Dorado field is one of the chief factors in creating an intimate 
 mixture of oil and water. This point is illustrated by the action of fluid 
 in a pumping well in the north end of the field. The superintendent stated 
 that with the valve on, the casinghead open (allowing gas to escape) no 
 emulsion was produced. With that valve closed, 60 per cent emulsion re- 
 sulted.
 
 60 EL DORADO, ARK., OIL AND GAS FIELD 
 
 It appears likely that the quantity of emulsion formed in wells with 
 high pressure will be reduced by diminishing the output, but this, if true, 
 would not be of economic importance in all instances. For example, an 
 operator stated that the production of one well making 16,700 barrels per 
 day through a 4-inch flow pipe, was reduced to 3,400 barrels per day by 
 inserting a %-inch choke. 
 
 Dehydration: 
 
 In most cases, El Dorado oil must be treated after it leaves the sep- 
 arator before the pipe line companies will accept it. At least four gen- 
 eral methods of treating emulsion have been tried in the El Dorado field 
 with satisfactory results: They are (1) the Tret-O-Lite System, (2) Cen- 
 trifugal machines, (3) Electric Dehydration, (4) the so-called "gun-barrel" 
 tank. 
 
 (1) The most common method of treating emulsion in the El Dorado 
 field is by the addition of chemical compounds. The best known of these 
 is Tret-O-Lite. This is a chemical which, when mixed with some oil-water 
 emulsion, causes the water to settle out, leaving clean oil. The cost of 
 treatment varies from 3 cents to 18 cents per barrel of clean oil, according 
 to the percentage of emulsion. Tret-O-Lite compounds are usually under- 
 stood to be essentially crude soaps or compounds of sodium and sulfonic 
 acid. The average cost is about 9 cents per barrel of oil treated. The 
 amount of Tret-O-Lite used varies from 10 to 70 gallons to every 1,000 bar- 
 rels of oil. Different methods are used to mix the Tret-O-Lite with the 
 oil. One company uses about 1,000 feet of 2-inch coil pipe through which 
 the emulsion and Tret-O-Lite mixture is pumped before being run into the 
 settling tank. The amount of Tret-O-Lite running into the coils can be 
 gauged by means of a glass indicator, before the mixing occurs. The water 
 settles into the bottom of the tank, where the water level is usually kept 
 about seven feet from bottom. A steam pipe open at its lower end extends 
 almost to the bottom of the tank and maintains the temperature at from 
 100 degrees to 110 degrees Fahrenheit. The introduction of live steam into 
 the settling tank should, however, be avoided, because it agitates the oil, 
 thereby retarding settling, and also increases evaporation. The clean oil 
 is drawn from an outlet pipe about two feet from the top of the tank and 
 runs into storage tanks by gravity. 
 
 One company uses an additional device to insure a more thorough mix- 
 ing of the chemicals and emulsion. This consists of two joints of 8-inch 
 pipe, about forty feet long and laid on the ground, with two unjointed pieces 
 of 2-inch perforated pipe placed inside from each end. The emulsion and 
 Tret-O-Lite mixture is pumped through one of the 2-inch pipes and inside 
 the 8-inch pipe and is forced out through perforations in the other small 
 pipe. The more uniform mixture is then pumped through coils on the 
 ground, to increase time of contact, before being run into settling tanks. 
 Steam coils are generally used to raise the temperature of the emulsion to 
 about 120 Fahrenheit. In order to maintain a constant feeding pressure, 
 it has been found desirable to feed the emulsion from the stock tank into 
 a 25-barrel tank at about the same level as the pump. By this method, a 
 reasonably uniform mixture with Tret-O-Lite is maintained. 
 
 (2) Centrifuge System is used to some extent in the El Dorado field. 
 Centrifuges or supercentrifuges, as the oil field types are commonly called, 
 are really enlargements of the cream separator with certain modifications 
 which adapt them to oil field use. They rotate at speeds which reach a 
 maximum of 17,500 revolutions per minute and develop tremendous sep- 
 arating forces. 
 
 In the El Dorado field the Magnolia Petroleum Company has installed 
 a 5-unit Sharpies plant for treating their emulsions. The total cost of in- 
 stallation, including equipment, labor and freight, is approximately $18,200. 
 The operating cost on this plant is not known, but on a similar plant in 
 another field, it is said to have amounted to $62 per day. This figure is 
 believed to be the minimum cost at which such a plant could be operated, 
 and it is probable that such a low average could not be expected over a 
 great length of time. 
 
 In this installation Tret-O-Lite is used in combination with the cen- 
 trifuge process when the percentage of emulsion is greater than 10. The 
 plant is 5-unit and the capacity ranges from fifteen to twenty-five barrels
 
 EL DORADO, ARK.. OIL AND GAS FIELD 
 
 61 
 
 per hour for each machine when treating oil* averaging about 80 per cent 
 emulsion. When using Tret-O-Lite in combination with the centrifuge, 
 four quarts are used to 100 barrels fluid. The following description is given 
 in a report by the Sharpies Specialty Company: 
 
 Plate XVIII. The Two-Unit Electric Dehvdrator on the Hearin Lease of the 
 Humble Oil Company. 
 
 "The emulsion is pumped from storage to the bottom of an elevated 
 supply tank which is equipped with a steam coil and Sarco Regulator for 
 heating. As the emulsion enters the bottom of the tank it rises through
 
 62 EL DORADO, ARK., OIL AND GAS FIELD 
 
 such salt water as may have accumulated from the emulsion and gradually 
 nils the tank, during which period it is brought up to a standard tempera- 
 ture of f'-om 160 to 170 degrees Fahrenheit. The pre-treatment of emul- 
 sion is essential and in fact, some emulsions may require the addition of 
 suitable chemicals, in order to give greater plant efficiency. 
 
 (3) The Electric Dehydrator This electrical method of treating emul- 
 sions has met with success in the El Dorado field. The Humble Oil & Re- 
 fining Company installed a two-unit plant in the south part of the field. 
 This installation is shown in Plate XVIII. On account of the high per- 
 centage of B. S. (85 per cent, in some instances), the rate of recovery of 
 oil was below normal for that process, the average capacity for ordinary 
 emulsions being 450 barrels per unit per day. Tests on these emulsions 
 have shown that they average about 68 per cent water. 
 
 The capacity of an electrical dehydrator usually varies from 300 to 
 1,200 barrels per day, per unit. The capacity is limited, because if too 
 much emulsion is run through the plant, the current would be short-cir- 
 cuited by the excessive water and the proper separation of oil and water 
 prevented. The emulsion remaining in treated oil is usually less than one 
 per cent. The electrical dehydrating process was invented by Dr. Fred- 
 erick G. Cottrell, former Director of the Bureau of Mines. The Petroleum 
 Rectifying Company gives the following description of the Electric Dehy- 
 drator: 
 
 "The Standard Cottrell apparatus consists essentially of the electric 
 treater and a settling or trap tank. The treater is approximately three feet 
 in diameter and ten and one-half feet high, made of galvanized iron, this 
 tank shell constituting one electrode that is 'grounded.' The other, or 'live,' 
 electrode consists of several circular discs, generally four discs eight inches 
 apart, mounted on a vertical shaft concentric with the treater shell. These 
 are slowly revolved by gearing from a small moter. This electrode carries 
 a voltage of approximately 11,000 and is properly insulated from the gear- 
 ing and the rest of the treater * * * *. Within the treater is a steam coil 
 for controlling the temperature of the emulsion undergoing treatment." 
 (This is usually about 135 degrees Fahrenheit.) 
 
 The emulsion is run through an electric field set up in the annular 
 space between the edges of the discs and the treater shell, where it is 
 broken up by the electric current. The water forms in large drops and 
 settles to the bottom by gravity, where it is automatically drawn off in a 
 continuous stream. The clean oil rises to the top and flows out to the 
 storage tanks. 
 
 The electric power-requirement for the two-unit installation mentioned 
 was about 2.76 kilowatts. The probable cost of generating electricity on 
 the lease is about 4 cents per K. W. H., making a total cost of about 11 
 cents per hour for the electricity needed to operate the two units. The 
 total cost of treating oil, considering various items such as steam, elec- 
 tricity, royalty, labor, repairs, interest and depreciation, has been found 
 to be from one to three cents per barrel of net oil, according to the report 
 issued by the Petroleum Rectifying Company. 
 
 (4) The so-called "gun barrel" tank which is sometimes used to de- 
 hydrate oil, is not satisfactory for use in the case of highly emulsified oil. 
 It is suited for settling out water held more loosely in suspension. 
 
 The apparatus consists essentially of a tank fitted with steam coils on 
 the bottom, a vertical wooden flume from top to bottom, a swing pipe con- 
 nected near the bottom, and an overflow connection near the top of the 
 tank. The oil is run into the flume at the top. It is conducted to the bot- 
 tom of the tank and comes in contact with the hot steam cores before mixing 
 with the other fluid. The oil-water mixture is broken up when passing up 
 through the hot fluid, the oil rising to the top and the water settling to the 
 bottom. The clean oil runs to storage through the overflow pipe. The 
 height of the water can be regulated by raising or lowering the swing pipe. 
 The excessive heating of the oil by this process results in considerable loss 
 by evaporation. 
 
 Natural Gas Gasoline: 
 
 As yet, there are no plants for the recovery of natural gasoline at 
 El Dorado. As the richness of gasoline in natural gas increases as the gas 
 pressure decreases, it would be desirable for operators who produce quan- 
 tities of gas to have tests made, and should they warrant it, install gasoline 
 plants. One operator reports that he extracts a portion of the gasoline 
 from the gas in a unique way. Gas is blows through the crude oil while
 
 EL DORADO, ARK., OIL AND GAS FIELD 
 
 LE<j 
 
 ELND 
 
 a Sucker Rod* 
 
 b Wortinq Barrel 
 
 C Collar 
 
 J iweoq* N,opl e 
 
 e St.nd.no V.lvt 
 
 f ChoVt 
 
 q Per-forationj m Trap 
 
 h StHlinas 
 
 > Inlet ?.pe 
 
 j Perforator in Liner 
 
 C Liner 
 
 I Tubtnq 
 
 m Tr.p 
 
 
 FIGURE V 
 
 Fig. 5. Sand Trap Used in Some of the Pumping Wells.
 
 64 EL DORADO. ARK.. OIL AND GAS FIELD 
 
 in a tight tank. He claims gasoline from the gas is absorbed by the oil and 
 thus silghtly raises the gravity of the crude. In some cases, a compar- 
 atively "dry" gas would absorb gasoline from a fairly light gravity oil. 
 Types of Oil Well Pumps: 
 
 In the El Dorado field, oil well pumps with composition cup plungers 
 are most commonly used. A few steel plunger pumps have been tried and 
 have gained some favor for handling the sand. Several companies have 
 used a home-made sand trap successfully in this field in combination with 
 the ordinary cup pump (see Figure 5) Instead of the standing valve being 
 placed immediately below the working valve, it is attached to a stand pipe, 
 generally %-inch in diameter. This stand pipe, which is also the inlet pipe, 
 is screwed into a choke of the proper size and threaded to receive a %- 
 inch pipe on both ends. The lower end of the inlet pipe consists of about 
 one joint of a %-inch pipe which is screwed into the choke below. The 
 choke is threaded on the outside so that it may be inserted between two 
 collars on the trap. The trap shell is usually made up of 3-inch pipe, if 
 for use with 2-inch tubing. The choke and pipe below it tend to prevent 
 the entrance of gas into the working barrel. The choke also serves as the 
 bottom of the second or upper sand trap. The oil first enters the liner 
 through perforations (j), then flows into the trap (m), through perfora- 
 tions (g) just below the choke (f). The oil passes downward between the 
 walls of the trap and (^he inlet pipe and up through the inlet pipe (i) to 
 the standing valve (e). Some of the coarse sand drops to the bottom of 
 the trap as settlings (h) before the oil enters the inlet pipe. In case the 
 pump stops operating, the settling sand will settle past the standing valve 
 and make it possible to resume pumping without a "wet job." These traps 
 must be pulled and cleaned periodically, but they are known to reduce. the 
 sand trouble. 
 
 A great many kinds of pumps designed to handle sand have been tried 
 at El Dorado, and some of them have given fair satisfaction under the try- 
 ing conditions. It is possible that a combination of the sand trap principle 
 and a packed steel plunger may give economical service. A packing gland 
 at the top of the pump barrel would probably lessen the amount of sand 
 that gets between the plunger and barrel. However, it is not always 
 feasible to introduce complicated contrivances into wells. Theoretically 
 serviceable pumps may prove failures, when tried out. Much sand is 
 pumped with the oil in some fields of the United States and it is not un- 
 reasonable to expect that the problem may be solved in this field. Operators 
 should experiment with different kinds of equipment until the most satis- 
 factory pump or attachment is found. 
 
 Pumps equipped with composition cups have generally proved more 
 satisfactory than steel plungers for pumping sand-free oil of light gravity, 
 on account of the pliability of the cups, which allow less leak-back of low 
 viscosity oil. The cups, however, are short-lived when considerable coarse 
 sand is produced. 
 
 Regular steel sucker rods are used by most of the operating companies 
 in El Dorado field. At least two concerns use wire lines instead of rods 
 for pumping. Sinker bars are used just above the pump to facilitate the 
 down stroke. The use of lines facilitates the pulling of cups and cuts 
 down the production expense caused by pulling. 
 Oil Recovery From Unconso!idated Sands: 
 
 The economical removal of oil from incoherent sands will vary consid- 
 erably with several factors. The viscosity of the oil is one of the main con- 
 ditions that affect the problem. It is necessary to remove a larger quan- 
 tity of loose sand when producing heavy oil than is essential for producing 
 light oil. The heavy oil is less fluid and drags more sand into the well 
 with it than does light oil. It is sometimes impossible to extract heavy oil 
 without also lifting large quantities of sand. 
 
 This subject has been discussed at length, in the case of heavy oils, 
 by Kobbe* and Suman.t In the case of light oil, it is probably better to 
 remove only enough sand with the oil to keep the oil stratum fairly free 
 from mud and waxy deposits. 
 
 *Kot>be, Wm., Recovering Oil from Unconsolidatcd Sands, Vol. LVI, Trans- 
 actions American Institute of Mining Engineers. 
 
 "\Suman, John R., Petroleum Production Methods, ft>. 282, 283.
 
 EL, DORADO, ARK., OIL AND GAS FIELD 6u 
 
 It is no doubt true in general that a large removal of sand with the oil 
 will increase the extraction of oil by lessening the friction offered to its 
 reaching the well. The cost of handling the sand must, of course, be a large 
 factor in determining the economical procedure. A considerable removal 
 of the sand with the oil may result in a small inverted cone-shaped cavity 
 forming at the well and in a slightly decreased density of sand near the 
 well. 
 
 The overlying formations at El Dorado appear to be rather loosely con- 
 solidated, with the exception of some minor lime strata and the roof of 
 the oil reservoir, therefore, may not stand up definitely above an extensive 
 cavity. The roof may generally follow the sand downward and maintain a 
 fairly constant sand density, or it may stand up lor a while and suddenly 
 collapse. Such collapse of .the rock overlying the oil sand has been known 
 to cause serious mechanical difficulty and decrease of production in fields 
 producing heavy oil. 
 
 Experimentation in each particular area or field is the only reliable 
 means of drawing correct conclusions, but in view of the known conditions 
 in El Dorado, it would seem inadvisable to remove any more sand than 
 is necessary to keep the sand around the well reasonably clean. Some op- 
 erators have becDme disgusted with screens and liners and have allowed 
 the sand to "heave" into the hole. When the production drops off consid- 
 erably, tools or bailer are run to clean out. There is no. definite informa- 
 tion at hand with which to compare the effectiveness of this practice with 
 the use of liners or screens. The amount of open hole below the shoe of 
 the water string would influence this practice, as cavings from the walls 
 of the hole may be a serious consideration in the case of high shut-offs. 
 
 It is believed that the gathering of clean sand around a liner will prob- 
 ably not offer much resistance to fluid movement. In fact, the loose sand 
 should be the more porous for the reason that it has no cementing material 
 in its pore spaces. Clean sand does not clog the perforations so that oil 
 cannot enter the liner, even though it bridges in them. Perforations up to 
 Vi-inch have been used in the El Dorado field. 
 
 Perforated Liners and Screen Pipe: 
 
 Perforated liners and screen pipe have been used in various ways at 
 El Dorado. A home-made screen was devised by close wrapping by ma- 
 chine of No. 10 gauge wire around a perforated pipe. One of these, after 
 being in a well only a short time, became plastered over with fine sand and 
 mud which shut out the production. Such a device will not give satisfac- 
 tion unless it is certain that no impervious material, such as mud, can ac- 
 cumulate on it. The spaces between the wire wrappings were first clogged 
 with fine sand and then with mud. Liners with inserted screens have been 
 tried and are used by some of the operators. These are not, in general, 
 satisfactory. 
 
 Practically all screens now manufactured have a wrapping of slots 
 which are keystone-shaped, in order to minimize the wedging of sand and 
 pebbles in the openings. Two makes of patented screen used at El Dorado 
 are made by wrapping "Keystone" wire around and soldering the wire to 
 perforated pipe. Another make has slotted "buttons" inserted flush into 
 large perforations in the pipe. The matter of selecting a suitable size for 
 screen mesh must be given considerable attention and it may vary some- 
 what in different localities of the field and in any well as the gas pressure 
 declines. The size of the openings is, of course, a matter of experiment in 
 the different areas. The finer meshes of screen have been the the rule 
 and will probably continue in use, as long as screens are considered useful. 
 
 At El Dorado, the liners and screens, when inserted very far below 
 the top of the sand, should be closed on the bottom to prevent the sand 
 and mud from "heaving" up into the liner. It may sometimes be advisable 
 to have the liner or screen blank for a certain distance above the bottom 
 of the hole. 
 
 Considerable difference of opinion exists among the operators regard- 
 ing a seal for the top of the liner. Although it is difficult to effect a tight 
 mechanical seal between a liner and water string, it is not difficult to ex- 
 clude the coarser sand by that means. A seal may also be of service in 
 holding the liner in place. In one case, where the perforations had been 
 clogged, an unsealed liner resulted in practically all of the oil passing up
 
 EL DORADO. ARK., OIL, AND GAS FIELD 
 
 between the liner and casing. It' a liner can be sealed at the top without 
 bridging sand above the perforations, it would be good practice to aid in 
 the easy removal of the liner when necessary to clean out. A canvas packer 
 is used at the top of the liner in some wells. One operator has decided that 
 the best system is to use a perforated liner fitted with a bell nipple on top. 
 
 It is believed that the finer sand and mud content of the oil stratum 
 should be allowed to have fairly free entrance into the wells, in order that 
 the clogging effect will be reduced. Any tendency of this oil to deposit 
 paraffin in formation or tubing, is evidently counteracted by the scouring 
 action of the sand. 
 
 In the declining period of a well's life, it may be found feasible to stim- 
 ulate the movement of fine sand and sludge through the liner or screen and 
 into the well. Several methods are known for stimulating wells. They in- 
 clude steaming, positive and, negative swabbing and the introduction of hor 
 oil. Washing with hot or cold water is sometimes done but the method 
 should be used w r ith great care, if at all. Excessive water is not beneficial. 
 Hot water, put in from the surface, may drive waxy sediment back into the 
 sand and redeposit them along a ring of sufficient cooling. Vigorous swab- 
 bing is not recommended on account of the ever present danger of draw- 
 ing in top, edge or bottom water and the danger of caving-formations. The 
 use of hot oil or distillate is probably best adapted to the removal of any 
 waxy sediment forming under conditions as found at El Dorado. The in- 
 troduction of hot oil melts the waxy sediment and also tends to render the 
 oil less viscous and thus permits a freer movement of oil sand into the 
 well. 
 
 If an abnormal quantity of sand flows into a well, it may become neces- 
 sary to temporarily raise the pump to prevent its sanding up or cutting out 
 of the plunger. 
 
 Flow Oil Through Tubing: 
 
 The general practice at El Dorado has been to "flow" wells as long as 
 they could produce reasonably large quantities of oil by this method. Some 
 of them flow as low as fifty barrels per day before being put on the pump. 
 A few operators are taking advantage of the gas pressure and are flow- 
 ing the oil through small tubing which is packed off at the surface or near 
 the shoe of the water string. This practice is economical and generally 
 keeps wells flowing for an additional period. Some operators put their 
 wells on the pump when the output has declined to 100 barrels per day 
 because pumps will increase the production. The high cost of pumping 
 more oil with large quantities of sand must be balanced against a quicker 
 return on the investment, but has the advantage of better protection against 
 drainage by neighboring wells. 
 
 Air Lifts for Raising Oil: 
 
 Lifting oil by means of compressed air jets is comi],>:u practice- in som^ 
 fields. When the fluid level in a well is high, due principally to water, any 
 lowering of fluid will aid in the recovery of oil, as discussed under Water 
 Conditions. Because compressing air is rather expensive and because 
 air lifts in wells tend to emulsify oil, the method may not always be adapt- 
 able. The production of water-free sandy oil by air would no doubt be 
 economical if there was a sufficient quantity of oil to allow of fairly con- 
 tinuous operation. The efficient lifting of liquids by compressed air calls 
 for about 35 per cent submergence, which would not be likely to exist for 
 a period long enough to justify air installations to produce clean oil. In 
 U. S. Bureau of Mines Bulletin 195. by A. W. Ambrose (referred to pre- 
 viously), a portion of an unpublished paper i>v E. W. \Vagy gives some 
 interesting data on compressed air lifting practice, to which the reader is 
 referred. 
 
 A well making sufficient water to cause an air lift to appear feasible, 
 should be repaired, if possible, in order to increase the oil production, de- 
 crease the water production and reduce the cost oi" lifting so 'much fluid, 
 An air lift must operate continuously to be practicable. When water is" 
 shut off, pumping of oil with air "by heads" is not practicable. There are 
 so many factors opposed to the lifting of several thou and barrels of water 
 with air. in order to obtain several hundred barrels of oil, that, first of all. 
 the possibility of shutting off the water without decreasing the oil produc- 
 tion should be considered. In other fields, much water was produced for
 
 EL DORADO, ARK., OIL AND GAS FIELD 67 
 
 several years, in order to produce some oil, after which the water was shut 
 off, with a resulting increase in oil production. Water often aggravates 
 sand trouble by settling and packing the sand. Incoming sand will not be 
 floated out by a water current as well as by an oil current of the same 
 velocity, because the oil is more viscous it has more "body." 
 
 The presence of dissolved air in the oil and gas lowers the gravity of 
 the oil by carrying off the lighter fractions. Air also dilutes the gas and 
 may ruin it for fuel use, and the energy necessary to extract a given amount 
 of gasoline from gas is thereby increased. 
 
 The air lift has been tried in only a few wells at El Dorado. The Clark 
 & Greer well on Section 17-18-15 started to make water and decreased in 
 oil production. The well was put on air and the oil production was in- 
 creased, due no doubt to a lowering of the fluid level in the hole. Although 
 several thousand barrels of fluid per day was removed, the fluid level was 
 apparently not greatly reduced. The water soon "killed" the gas and the 
 oil production stopped. Even though the water could have been removed 
 to a low level as fast as it entered the well, its steady flow through the oil 
 stratum would have prematurely cut off the oil supply. 
 
 Vacuum Pumping: 
 
 In some fields, vacuum pumps are applied to the well in order to stimu- 
 late production and to enrich the casinghead gas. The vacuum pump is 
 attached to a lead line from the casinghead and is set where the applica- 
 tion of power is convenient. This system of pumping is only employed in 
 fields where the production has declined to such a point that it is unprofit- 
 able to pump the wells without some stimulation of production or an en- 
 richment and increase in casinghead gas. 
 
 Although vacuum pumping has not as yet been tried at El Dorado, the 
 subject is here mentioned as of possible future importance in that field. 
 Its application may not be found feasible, but if used it should be applied 
 cautiously in accordance with well-directed experiments. The haphazard 
 use of Vacuum has created ill feeling among operators in certain fields. 
 Vacuum has drawn water into wells, with harmful results. 
 
 Regardless of the generally incoherent condition of the sand at El Do- 
 rado, vacuum pumping may possibly find useful application, inasmuch as 
 a suction of fourteen pounds per square inch would probably influence 
 sand movement no more than a positive gas pressure of fifty or one hundred 
 pounds per square inch. This principle does not apply to water infiltration, 
 however, and high vacuums may rapidly draw in water. The vacuum 
 shown on the gauge at the surface is not the actual vacuum applied to the 
 movement of oil, as friction reduces the vacuum by the time it is applied 
 to the sand. In applying vacuum, it is probably best to start with a low 
 vacuum and increase gradually. Each well, however, may be a special 
 problem. It is reported that in some cases high vacuums draw less oil 
 than low ones, and wells can occasionally be increased by lowering the 
 vacuum to a certain point. The rapid by passing and loss of gas reduces 
 the total assistance of its expansive force for oil extraction. 
 
 It is sometimes found that vacuum pumping does not materially in- 
 crease production. When the productive sand is coarse and heavy, the 
 wells will not "sand up" so readily by vacuum pumping. Some very di- 
 verse phenomena have been noted under apparently similar conditions in 
 vacuum pumping. There is, no doubt, much to be learned of the action of 
 vacuum under varying underground conditions. While the use of vacuum 
 pumping will increase the ultimate extraction of oil in some fields, where 
 conditions are suitable, its successful application is doubtful at El Dorado. 
 
 Power for Pumping: 
 
 The power most extensively used in the El Dorado oil field for pump- 
 ing purposes is the gas engine. Various types of gas engines are used. 
 They are equipped with magneto, "wyco" and hot point ignition systems, 
 which are discussed under the subject of "Drilling Methods." The steam 
 engine is too expensive for pumping individual wells, unless the central 
 power of a jack line system is operated by that means. It should be used 
 in such a manner only when gas engines, oil engines and electric motors 
 are not economically usable. 
 
 The central power system with jacks has not as yet been installed in 
 the El Dorado field. The use of jacks is usually practicable in depleted 
 fields where there is very little trouble from sand. It does not now ap-
 
 6S EL DORADO, ARK., OIL AND GAS FIELD 
 
 pear likely that groups of wells will be operated by jack lines from cen- 
 tral powers, on account of the frequent necessary work on the wells clue 
 to sand troubles. If this condition is overcome sufficiently, jack systems 
 may be profitably operated in conjunction with a cheap portable power unit 
 for pulling, such as a tractor fitted with a hoisting drum, or even by in- 
 dividual engines which are left at the well. In this connection, full con- 
 sideration must be given to the probable life of El Dorado wells. If the 
 wells produce only a short time, it might not pay to change from individual 
 power to jacks. In general, the principal factors governing the selection 
 of suitable pumping systems are amount of production, depth of wells, size 
 of tubing, gravity of oil, topography of the country, relative location of the 
 wells and the speed of pumping desired. 
 
 Counterbalances and Tail Pumps : 
 
 Counterbalances on the beams of pumping wells have not as yet been 
 used in the El Dorado field. It is well known that they can be used to 
 advantage in any field, and it is recommended that operators install them. 
 
 Counterbalances are used to balance the dead load and assist in main- 
 taining uniform turning motion. This cuts down idle time due to parted 
 rods. The primary object of installing them is to decrease the power con- 
 sumption, idle time and -rod breakage. Where the cost of gas is only of 
 secondary importance, suitable counterbalance will soon pay for itself by 
 decreasing the wear on the gas engine and rods. The counterbalance also 
 tends to reduce the amount of emulsion in production, by causing the rods 
 to move more smoothly. Emulsion is, in some cases, iormed by the churn- 
 ing action produced by leak-backs past damaged cups and valves and a 
 portion of the damage is due to the vibration of the rods. 
 
 One of the most efficient counterbalances is a concrete block, supported 
 from an extension of the walking beam by a stirrup. The position of the 
 stirrup on the beam may be changed, in order that the leverage may suit 
 the- conditions of the load. Guides must be provided to prevent tjie con- 
 crete block from swinging. 
 
 Except in the case of a few line pumps, beam-operated pumps have 
 not yet been installed. The tail pump is usually installed between the 
 "sampson post" and "pittman," or on an extension of the beam, so that the 
 same power pumping the well operates the tail pump. The upstroke of the 
 tail pump is actuated by the weight of the descending rods, but its down 
 stroke does not assist in the lifting of the rods. Some of the lead lines are 
 long and the frictional resistance is considerable. Some flow tanks are 
 considerably higher than the wells and additional power is required to 
 force oil to the tank. The load on the well pump can be appreciably de- 
 creased by the use of a tail pump which requires little or no extra power 
 to operate. 
 
 Conclusion 
 
 In studying conditions at El Dorado, it was found that the character of 
 the reservoir strata is somewhat different from the average field. With 
 respect to the association of oil and lower water, it is hoped that the ideas 
 expressed herein will form the basis of continued investigation by others. 
 The underground relation between the two liquids is one of the most im- 
 portant questions to solve. Without some accurate knowledge on this sub- 
 ject, the handling of wells becomes largely a matter of guess work. "Cut 
 and try" methods are necessary to gain information as well as produc- 
 tion, but experiments in blowing and deepening wells should not go beyond 
 reasonable limits. The drilling and production practices in the El Dorado 
 field have been generally wasteful, much of which could have been avoided 
 by the application of good engineering. 
 
 The two main factors affecting the recovery of oil in the El Dorado 
 field are water and loose sand. Wells that make considerable lower water 
 should be plugged in the b.ottom with cement, regardless of whether there 
 is a known impervious parting between the oil and bottom water. The top 
 of the plug should be at least two feet above the probable top of the water. 
 Best results with cement will be obtained by the tubing method, under a
 
 EL DORADO, ARK.. OIL AND GAS FIELD 69 
 
 pump pressure of at least 500 pounds per square inch. It is recommended 
 that a wooden plug be used in the tubing ahead of the cement and that a 
 packing head with a relief valve, be used at the surface. 
 
 At El Dorado, rotary drilling has failed to determine the safe depth 
 to drill wells. Core-barrelling has been unsuccessful in this field, on account 
 of the unconsolidated character of the oil sand. It is believed, however, 
 that as core-barreling is successful in soft sands in other fields, that bet- 
 ter results with core barrels can be accomplished at El Dorado. It is rec- 
 ommended to drill wells in with cable tools after cementing the water 
 string. The driller may "feel his way" into the sand and avoid drilling too 
 deep. 
 
 The position of each well with respect to the structure should be borne 
 in mind and down-dip wells with a contour-control as low as 1,935 feet 
 below sea level, should barely penetrate the top oil stratum, lest the 
 water-bearing portions of the strata be opened up after producing a short 
 time. 
 
 The problem of handling sand in pumping wells may be solved to a 
 great extent by experimenting with steel plunger working barrels designed 
 to handle sand and by the use of sand traps. The control of flowing wells 
 is a matter of utmost importance. Wells must be restricted in their flow, 
 in order to avoid "self deepening" and premature entry of water. 
 
 Production methods used by various operators in the field differ widely. 
 It is suggested that operators study the results obtained by other pro- 
 ducers who are trying new methods. Informal discussions between produc- 
 tion men of the various companies should be encouraged. It was found 
 that some operators were not fully informed as to the methods in success- 
 ful use by their neighbors. 
 
 Uniform systems of cost accounting should be adopted in order to cor- 
 rectly compare the efficiencies of different operations and appliances. The 
 free exchange of ideas and open discussion in a spirit of co-operation can- 
 not fail to be of mutual benefit. 
 
 Sufficient funds should be provided for a Conservation Commission com- 
 posed of experienced and competent oil men, with ability to cover all of 
 the important inspection work of the field. The present system of raising 
 money by collecting fees is inadequate and unsatisfactory. The amount of 
 money necessary to support an adequate conservation force will be insig- 
 nificant as compared to the gain to the industry. 
 
 The Commission should inspect and record all vital operations in wells, 
 such as test of water shut-off, special mudding operations, plugging bot- 
 tom to shut off water, or plugging to abandon. Cement plugs should be 
 tested for hardness, thickness, and location. The Commission should make 
 underground studies and render decisions in writing to the operators, with 
 respect to where water should be shut off and the depths of wells. When 
 the companies employ engineers to study underground conditions, they, in 
 consultation with the state representatives, can discuss matters of dispute 
 and reach satisfactory and logical conclusions. 
 
 Operators should welcome such a plan, as they would be protected 
 from flooding with water by inefficient and inexperienced operators, and at 
 the same time there should be' preserved certain valuable facts regarding 
 the wells that might overwise be lost. 
 
 The possibility of shallower and deeper oil sands of importance should 
 be considered before a definite plan is adopted for drilling up the field. As 
 outlined in the body of the report, the proper use of mud fluid and cement 
 is recommended. It appears logical to test these possibilities before aban- 
 doning present wells on account of depletion. 
 
 Efforts should be made to reduce the formation of emulsion both un- 
 derground and at the surface. If the wells and pumps are in good me- 
 chanical condition, emulsions will not form so readily. Wells that flow 
 water with oil and gas are likely to emulsify, despite all efforts, but prop- 
 erly designed separators will aid in keeping down the amount of emulsion 
 formed. 
 
 Swabbing is not adaptable to El Dorado field, because of the loose 
 sands. It should be limited to the few instances where wells can only be 
 rid ol mud and water and their flow started by swabbing. 
 
 It is very doubtful if vacuum pumping would be successful at El Do- 
 rado.
 
 70 EL DORADO. ARK.. OIL AND GAS FIELD 
 
 The spacing of wells should be about nine acres per well (627 feet dis- 
 tance i, in view of the present (November, 1921) price of oil. 
 
 Other production economies, such as tail pumps, counterbalances, mul- 
 tiple pumping with jack lines, use of tubing catchers, use of low-pressure 
 burners to conserve the rapidly diminishing gas supply, and discard of 
 steam power or proper installation and insulation of boilers and steam lines 
 are recommended for use where adaptable. 
 
 Concerted efforts should be made to reduce oil losses due to evapora- 
 tion, seepage and other mechanical means. Practically no gas should be 
 allowed to waste. Its use for moving oils into the wells and its use for 
 fuel, render it highly important in the recovery of oil. Surface conserva- 
 tion is second in importance only to underground conservation.
 
 EL DORADO. ARK.. OIL AND GAS FIELD 71 
 
 El Dorado Oil Field in Arkansas-Dis- 
 covery and Development 
 
 The El Dorado oil field in Arkansas was discovered by the Constantine 
 Refining Company when their Armstrong No. 1 well in Sec. 1, T. 18 S., R. 
 16 W., struck an immense flow of gas, estimated at 40,000,000 cubic feet 
 a day, and a small quantity of oil. The oil men of the mid-continent region 
 paid comparatively little attention to this discovery for several months, 
 although a few companies, acting on the advice of geologists, leased some 
 land near the gas well, but when a well drilled by Mitchell & Busey in Sec. 
 31_, T. 17 S., R. 15 W., came in on January 10, 1921. with a flow of about 
 1,500 barrels of oil a day and perhaps ten times that much water, there was 
 a stampede for the field. Leasing and drilling were pushed with an in- 
 tensity so tremendous that, in spite -of several months' delay in getting 
 an adequate pipe line outlet for the oil produced, the field was developed 
 with remarkable rapidity. The oil sand is only about 2,150 feet below the 
 surface, and the rocks above it are mostly beds of shale and clay that are 
 easily penetrated by the rotary drill. Wells that gave a large output were 
 the rule rather than the exception, several yielding more than 19,000 bar- 
 rels a day. although most of these wells produced much salt water with 
 the oil. The output reached about 82,000 barrels a day during the week 
 ending August 20, 1921. but declined rapidly to about 32,000 barrels a day 
 during the week ending March 11, 1922. Since then the output has in- 
 creased slightly. 
 
 Studies of the Geology of the Field: 
 
 Field studies of the geologic structure were made 'in the summer of 
 1921 by W. W. Rubey, L. G. Mosburg and H. W. Hoots, of the United States 
 Geological Survey, Department of the Interior, and office studies were 
 afterward made by K. C. Heald and W. W. Rubey. The primary purpose 
 of these studies was to learn the conditions under which oil is most likely 
 to occur in southern Arkansas. The investigation was afterward extended 
 to ascertain the relations of the oil to the water in the strata for the in- 
 iormation of the engineers of the Bureau of Mines, who were working in 
 co-operation with the State. 
 
 Each oil-yielding district has its own peculiarities, and the rules that 
 may guide prospecting in one area may not apply to another. The great 
 number of test wells that have been drilled in southern Arkansas without 
 finding oil in large quantity except in the El Dorado field, show either that 
 the oil pools in this region do not bear the same relations to anticlinal 
 structure that they commonly bear elsewhere in the mid-continent oil field 
 or that geologists have not learned how to locate the anticlines in this 
 field by studying the surface formations. If the geologist is without definite 
 rules to guide him in discovering oil pools, his usefulness is much less than 
 it otherwise would be, and the operator must hunt for new pools blindly, 
 so that his chances of success will be reduced and the average outlay for 
 each now pool he may find will be greatly increased. Random drilling has 
 discovered many great oil fields, and persistent prospecting without geo- 
 logic guidance would ultimately find every pool, just as a blind-folded man 
 could find almost any object he sought if he sought long enough, but this 
 is no reason why the blindfold should not be removed if it can be removed. 
 One of the most effective aids in locating undiscovered pools is an accu- 
 rate, thorough knowledge of the conditions in fields that have been de- 
 veloped, and any one who hopes to find new pools in southern Arkansas 
 should study the El Dorado field and the fields to the south in Louisiana. 
 
 Structure of the Field: 
 
 The geologic structure of the El Dorado field is unlike that of any 
 other known field of similar size. The studies made covered only the 
 northern part of the producing area, but there is no reason to think that 
 the structure of the southern part is materially different. If the sand, 
 clay and gumbo could be stripped off the producing bed in the area cov- 
 ered by the map no large dome or great anticlinal arch would be seen. The 
 surface of the oil sand is so nearly level that it might remind one of gently
 
 EL DORADO. ARK., OIL AND GAS FIELD 
 
 R.15W. 
 
 Structure contours on top of 
 Nacatoch sand Cashed lines, 
 > position inferredihachurer; 
 line indicates structural depres- 
 sion. Contour interval lOfeet 
 Datum is mean sea level 
 
 Depth below sea level of cap rock above 
 middlt of pay sTreSk.MacatOCh 
 
 sano 
 
 33 
 
 *&., fa 
 
 jffr7J-fr 
 
 w.rLl fa\^ 
 
 // /** 
 
 .'-55S' 
 
 
 
 U. & GEOLOGICAL SURVEY 
 
 GEOLOGIC STRUCTUHE OF NORTHERN PART OF EL DORADO OIL FIELD. ARKANSAS 
 
 BY t C HEALD AND W. W RUBEY
 
 EL DORADO, ARK., OIL AND GAS FIELD 73 
 
 rolling prairies or of meadows made up in part of smoothly rounded knolls 
 and swales or hollows whose slopes rise in even, sweeping curves. The 
 evenness is interrupted by a number of low, almost vertical cliffs that mark 
 faults where the rock has been broken and one side of the break has risen 
 from one to thirty feet above the other. There are probably a great 
 many more of these breaks than are shown on the map. Almost without 
 exception they trend northeastward, forming a sharp angle with the longer 
 axis of the field, and most of the low folds that vary the flatness of the sur- 
 face of the oil sands also trend northeastward. 
 
 The oil sand rises higher in Sec. 1, T. 18 S., R. 16 W., than elsewhere 
 in the part of the field that has been mapped. Not enough wells have been 
 drilled in this part of the field to enable the geologist to work out its struc- 
 ture in detail, but it seems more nearly anticlinal than the narrow oil- 
 yielding area that borders it on the northeast, east, and southeast. The 
 few well records available indicate that in this part of the field there is 
 a real dome on which the beds dip gently to the east and more abruptly 
 to west and southwest. The wells on the dome yield gas and a little oil. 
 Between this dome and the oil-yielding belt to the east there is a rather 
 broad area over which the structure has not been worked out, so that the 
 impression of flatness in that area given by the map is unjustified. 
 
 The structure in the area west and south of the gas-yielding dome, in 
 Sec. 1. is not known, but the few records that are available show that the 
 oil sand there is fully as high as it is in the productive pr.rt of the oil 
 field. 
 
 A study of well records in areas east and west of the El Dorado field 
 shows^that this field is not upon a pronounced regional uplift, although there 
 may be~a slight bulge or gentle arch in the El Dorado region. The strata 
 dip gently to the east and southeast over most of southern Arkansas. If 
 the El Dorado field is on a regional bulge or uplift there is a synclinal de- 
 pression west or northwest of it. A flattening of the regional dip was de- 
 tected but no true syncline. Furthermore, if the field were an uplift the 
 strata immediately east of it would probably show steeper dips than are 
 common in this region, but no suggestion of such steep dips was found. 
 The location of this field is therefore not controlled by the manner in which 
 the rocks are folded. There is no true major anticline here, and the minor 
 folds did not control the distribution of the oil, although the gas in this 
 pool does tend to concentrate in arched or domed areas. The parts of the 
 field in which, as shown by the map, the structure is anticlinal lie in a 
 sinuous belt that trends in general northward through the center of Sec 31, 
 T. 17 S., R. 15 W., including about 40 acres in the NW%, Sec. 5. T. 18 S.. 
 R. 15 W. ; about 60 acres in the northeast corner of the same section: about 
 60 acres in the north-central part of Sec. 8, T. 18 S., R. 15 W.; and about 
 100 acres in the southeast corner of Sec. 7. T. 18 S., R. 15 W., besides the 
 gas-yielding dome in Sec. 1, T. 18 S., R. 16 W. In no one of these areas 
 are there oil wells that show productivity above the average or the free- 
 dom from water trouble that might be expected if the segregation of oil 
 were controlled by anticlinal structure. If the dates of completion and of 
 average decline in initial production are taken into consideration in order 
 to compensate for interference from adjacent producers, the wells in these 
 anticlinal areas are perhaps a little above the average for the entire field, 
 but this initial production is not higher than that of wells in adjoining syn- 
 clinal areas. 
 
 On the other hand it can not be said that in this field there is no rela- 
 tion between geologic structure and the accumulation of oil, for structure 
 includes both folds and faults, and the faults were probably influential in 
 forming the pool. Nearly every area of high productivity in the oil-yielding 
 belt here considered is traversed by one or more faults. A ftrip of richly 
 productive territory does not border each fault shown on the man, but 
 here and there along almost every fault there is a spot of unusual rich- 
 ness. 
 
 The direction and arranegment of the faults, and the shapes of the 
 low folds that accompany some of them, probably indicate the presence of 
 a large fault or zone of faulting in the beds deep below the Nacatoch sand, 
 trending about N. 15 \V. The structure shown by the oil sand there must 
 have been produced by lateral movement along this fault, the strata east 
 of it moving northward relative 'to the strata west of it.
 
 EL DORADO. ARK., OIL AND GAS FIELD 
 
 How the Pool Was Formed: 
 
 The Marlbrook marl is believed to be the source of the oil in this field, 
 and the accumulation of enough oil in the Nacatoch above the Marlbrook to 
 form a commercial field is probably due to a happy association of a source 
 of oil, channels through which it could migrate, and a good reservoir bed. 
 Oil was probably not formed everywhere in the Marlbrook, at least not in 
 great volume, but in favored spots where it was laid down in shallow 
 water, and possibly raised above the sea from time to time, the conditions 
 were right for the deposition and preservation of oil-forming matter. In 
 any event, in some places the Marlbrook appears to have supplied large 
 amounts of oil to the overlying Nacatoch sand, and in others, where the 
 structure is seemingly quite as favorable, it has supplied little or none. At 
 El Dorado the zone of faults crossed a productive area in the marl. The 
 oil moved up along the fault planes and accumulated in the upper part of 
 the Nacatoch sand. Pronounced anticlinal folding and faulting and a rich 
 spot in the Marlbrook would together have produced ideal conditions for 
 the accumulation of oil, and under such conditions the water trouble that 
 has been the curse of the El Dorado field would not have appeared. The 
 beds of sandstone lie so flat, however, that the oil they contain does not 
 saturate them to any great thickness; but instead it is found in thin 
 layers at the tops of several beds in the upper part of the Nacatoch, and 
 the remaining parts of these beds are filled with salt water. The gas being 
 more mobile than the oil has migrated to the more prominent domes and 
 has excluded most of the oil and the water from certain thin beds of sand- 
 stone under the arched areas. 
 
 If the formations just above the Nacatoch had contained porous sand- 
 stones the oil, as it moved upward along the fault planes, would probably 
 have formed small pools in them, for the faults are not limited to the beds 
 below the top of the Nacatoch, but certainly cut the Arkadelphia clays, 
 although these beds contain few sands. The faults may cut also the Mid- 
 way beds, although this supposition can not be definitely verified by the 
 well records, but no evidence was found to indicate that they cut the 
 Wilcox. 
 
 Instead of originating in the Marlbrook the oil possibly may come from 
 a much deeper formation, such as the Brownstown marl, the Eagle Ford 
 shale, or the Lower Cretaceous beds. The depth of these formations below 
 the Nacatoch is no obstacle to the migration of the oil, for the faulting 
 that cuts the Marlbrook must also cut them, and if it could furnish chan- 
 nels for upward migration from the Marlbrook to the Nacatoch it could 
 almost as easily furnish channels for migration from the deeper beds. If 
 the oil came from the Brownstown marl, there may be chances of finding 
 oil reservoir beds in this formation or adjacent to it, and if it came from 
 the Eagle Ford shale there is a good chance of obtaining it from the Blos- 
 som and Woodbine sands. 
 
 If the oil came from the Marlbrook marl, however, the chances of ob- 
 taining it from underlying formations are not exceptionally good, although 
 these lower formations should not be utterly condemned. The records of 
 other fields that draw oil from Upper Cretaceous formations prohibit such 
 a blanket condemnation, for practically all fields that have yielded either oil 
 or gas in notable amounts from the Nacatoch sand and have yielded much 
 greater amounts from either the Blossom or the Woodbine sands, or both. 
 The lack of anticlinal structure at El Dorado, however, offsets this favorable 
 feature. W T here oil is found in the Blossom or the Woodbine there is 
 either pronounced regional uplift or strong anticlinal folding. In the Caddo 
 and De Soto-Red River districts there are both. In the El Dorado district 
 there is neither. The conditions that are associated with oil pools in 
 northern Louisiana, and to which the formation of those pools is presum- 
 ably due, are therefore lacking here, and production from the deep beds 
 can not be counted on. Nevertheless, the deep sands should be tested. The 
 most promising locality for a deep test well, so far as the map shows, is on 
 the west side of the gas-yielding dome in Sec. 1, T. 18 S., R. 16 W. The 
 very center of the section seems to be a good location for such a test well, 
 but as it is desirable to make a test for oil in the Nacatoch at a place 
 west of the gas-bearing area, a location 800 feet west of the center of the 
 section would probably be preferable.
 
 EL DORADO, ARK., OIL AND GAS FIELD 75 
 
 Oil and Gas Above the Principal "Pay" Sand: 
 
 A few wells in the El Dorado field have reported "showings" of oil or 
 gas in beds in the Midway formation. The few reports that traces of oil 
 have been found in these beds might be discredited, for enough oil to give 
 a rainbow-colored film on the drilling water might accidentally get into a 
 well, but not traces of gas, and it therefore seems evident that at least 
 one bed in the Midway formation carries some oil and gas. This bed may 
 lie about 1,150 feet below the surface over most of the field, or about 970 
 feet above the Nacatoch sand. A number of sands in a zone 200-300 feet 
 thick may carry this shallow oil. The wells in which it is reported do not 
 lie on any of the faults that have been mapped or very near them, a fact 
 which indicates that the oil probably did not rise along those faults. 
 
 Reported showings of oil or gas in a number of wells that have been 
 drilled within a radius of forty miles of the El Dorado field suggest that an 
 oil-bearing sand may lie at the base of the Midway formation, which in the 
 El Dorado field is from 575 to 625 feet above the Nacatoch. No careful 
 tests of these shallow beds seem to have been made in the field, in spite 
 of the very apparent need for such tests. Small water-free wells that would 
 draw oil from a bed not more than 1,200 feet below the surface would prob- 
 ably yield greater net profits than the more spectacular but less reliable 
 wells that get oil from the underlying Nacatoch sand. Tests of the shallow 
 sands should be made very carefully, for the gas in them is evidently 
 low pressure, and it would be easy for one to drill through a thin oil or 
 gas-bearing sand without suspecting its presence. 
 
 Possible Extensions of the Field. 
 
 In the part of the field covered by this study the location of highly pro- 
 ductive wells near faults suggests the desirability of drilling in the south- 
 west corner of Sec. 7, T. 18 S., R. 15 W., and in the adjoining territory in 
 Sees. 12 and 13, T. 18 S., R. 16 W. The field may probably also be ex- 
 tended in the SE% SE^i Sec. 32, T. 17 S., R. 15 W., and there seems to be 
 no indication that the producing territory will not also include parts at 
 least of the SW% Sec. 33, T. 17 S., R. 15 W., and of the NW&, NW%, Sec. 
 4, T. 18 S., R. 15 W. A well in the NW*4 Sec. 7, T. 18 S., R. 15 W., should 
 yield either oil or gas, particularly in the eastern part of the quarter sec- 
 tion. The same is true of Sections 18 and 19 in the same township. 
 
 A number of test wells should be drilled west of the gas-bearing area, 
 for oil-bearing beds may possibly border the gas-bearing beds on the west 
 and south as they do on the north and east. Suggested locations for test 
 wells are the northeast corner of Sec. 2, T. 18 S., R. 16 W., the center of 
 the N% Sec. 2, T. 18 S., R. 16 W., and the center of the N% Sec. 12, T. 18 
 S., R. 16 W. 
 
 The extension of the field to the south of its present limits is to be 
 expected, and determined prospecting to discover a northward extension is 
 also justified by the peculiar type of structure. Operators should not accept 
 a single dry hole as limiting the field in these directions. The producing 
 territory at the present north margin of the field can probably be extended 
 westward. 
 
 Possibility of Similar Fields Elsewhere in Southern Arkansas. 
 
 Parallel belts of faults separated by areas almost unfaulted may occur 
 in southern Arkansas as they do elsewhere in the mid-continent region, 
 notably in northern Oklahoma and southern Kansas. If such a belt exists 
 within a few miles of El Dorado the other favorable conditions that com- 
 bined to produce the El Dorado pool probably also exist there and a field 
 much like the Ei Dorado field may be developed. Because of this probability 
 the following suggestions are made. 
 
 1. If gas in volume is encountered in a wildcat well the search for 
 oil should be continued by wells drilled east, northeast, or southeast of the 
 gasser. 
 
 2. If oil is encountered in a wildcat well the extension of the oil-yield- 
 ing area should be sought by other wells drilled either north or south of 
 the discovery well. 
 
 3. Gas pressure should be conserved by shutting in gas wells. The 
 maintenance of the high gas pressure will help to promote greater extrac- 
 tion of oil and to prevent water trouble.
 
 76 EL DORADO, ARK., OIL AND GAS FIELD 
 
 The chances for finding new fields are not limited to zones of faulting, 
 for there are probably anticlines in southern Arkansas fully as strongly 
 developed as those on which the Homer and Bellevue fields of Louisiana 
 are located. Even if some of the conclusions here presented may be ques- 
 tioned, other oil fields will no doubt sooner or later be discovered in southern 
 Arkansas, for in view of the showings of oil obtained in widely scattered 
 wells in this broad region it would be unreasonable to believe that there is 
 only one place in it where the conditions are favorable to the formation of 
 an oil pool. 
 
 Description of the Producing Bed: 
 
 The Nacatoch sand in the El Dorado field is about 180 to 190 feet thick. 
 The upper part is principally sand, but the formation also includes shaly 
 sandstone and streaks of gumbo and shale. The lower part varies from 
 slightly calcareous shale to hard limestone, although it generally contains 
 some thin sandy layers. 
 
 The top of the sand is commonly marked by hard streaks called "rock" 
 'by the drillers. At some places these hard streaks are absent, and drillers 
 who depended on them to indicate the top of the pay sand drilled deep into 
 the sand before they realized that they had reached the oil-bearing bed. In 
 fact, the drillers of the Busey well, commonly considered the discovery well 
 of the field, drilled through the bed that yields most of the oil produced 
 from the surrounding wells without recognizing it and obtained oil from 
 a lower pay streak in the sand. 
 
 There are at least three pay streaks in the upper part of the Nacatoch. 
 No one of these three streaks appears to extend through the field but the 
 middle one, which is about forty feet below the top of the sand, is nearly 
 continuous and yields most of the oil. Producing beds both higher and 
 lower than the middle one have made good wells, but these other producing 
 beds appear to be very patchy or perhaps they have not been adequately 
 tested, for comparatively few drew oil from them. The gas well drilled by 
 the Constantine Refining Company, which was the real discovery well of 
 the field, obtained its gas from a bed that lies about forty feet below the 
 bed which is yielding oil in wells to the east. 
 
 In all the pay streaks oil seems to be present only in the topmost few 
 feet of the sand and is everywhere underlain by salt water. Salt water is 
 also closely associated with the gas in the gas-yielding part of the field. 
 Unless a well is completed with the utmost care this water flows from it 
 with the oil and gas from the day it is completed until water flooding causes 
 its abandonment. This water is much more difficult to combat than the 
 water in most pools, because there is no such thing in this field as "edge 
 water," which is restricted to the margins of the producing area. So far 
 as salt water is concerned this field may be said to be all "edge" and each 
 well is a problem in itself. 
 
 There is no evidence that the Nacatoch is either thinner or more shaly 
 near the edges of the field than elsewhere. It is undoubtedly much more 
 shaly in some places than in others, but no relation between the yield of 
 oil and the percentage of clean sand could be determined. 
 
 Methods Used in Constructing the Map: 
 
 The records of wells drilled with rotary tools are notoriously poor and 
 afford very unreliable correlations. In the El Dorado field comparisons and 
 correlations are particularly hard to make, because the top of the Nacatoch 
 sand varies so little in evelation throughout the field and because no sin- 
 gle bed can be easily and certainly recognized everywhere. The results pre- 
 sented on the map are admittedly open to challenge, but they represent 
 very careful and painstaking work the best that can be done with the 
 data available. 
 
 The correlation of the beds struck in different wells was first attempted 
 solely by noting the relative positions of the beds of sandstone, limestone 
 chalk, and gypsum recorded by the drillers. The results of these correla- 
 tions were not satisfactory. Next, the "rocks" recorded by the drillers were 
 colored distinctively on the plotted well logs and were found to furnish a 
 good tie between many of the wells. However, to make satisfactory corre- 
 lations it was found necesary to assign characteristic symbols or colors to 
 every term employed by the drillers. The record of hardness was heloful. 
 "Boulders" were in places distinctive. Some of the "pack sands" could be 
 correlated ' between two or more wells. Shale and gumbo were distin-
 
 EL DORADO. ARK.. OIL AND GAS FIELD 77 
 
 guished, and although the usage of the drillers was not uniform their use 
 of these terms furnished a valuable clue for many areas. 
 
 The work thus done permitted the recognition of small faults shown on 
 the map. These faults would have been indicated by the evidence afforded 
 by the oil sands, but this indication had to be confirmed in the upper part 
 of the section. In a record of a well drilled across a normal fault a part of 
 the stratigraphic section is missing, and, conversely, in a record of one 
 drilled across a reverse fault a part of the section is repeated. In parts of 
 the map that are based on comparatively few well records the structure 
 appears to be much smoother and simpler than it is elsewhere, but if more 
 records had been available these apparently simple areas would no doubt 
 prove to be much more complex. 
 
 Character of the Oil: 
 
 Detailed analyses of the oil from the El Dorado field, published by the 
 United States Bureau of Mines November, 1921, show that its gravity is 
 about 34.2 Baume, and it contains about 30 per cent of gasoline and naphtha 
 and 13 per cent of kerosene, the remainder being gas oil and lubricating oil.
 
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 EL DORADO. ARK.. OIL AND GAS FIELD 
 
 Geology of the El Dorado Field and Some 
 Mistakes in Drilling Methods 
 
 (Prepared by the TJ. S. Geological Survey) 
 
 Of the many wells that have been drilled in south-central Arkansas for 
 oil, several apparently stopped short of the sand that yields the oil at El Do- 
 rado, in Union County, and the greater number did not reach the sand 
 that yields oil in the Haynesville field, in Claiborne Parish, La., is the 
 opinion of the United States Geological Survey, Department of the Inte- 
 rior. Furthermore, practically all drilling has been done with rotary tools, 
 a method which not only yields inaccurate records of the formation pene- 
 trated but which also requeutly prevents the recognition and testing of 
 oil sands that may be drilled through. 
 
 Several sands in northern Louisiana, below the Nacatoch, have pro- 
 duced much more oil than the Nacatoch, and in some of the fields the Naca- 
 toch is practically barren, in spite of the immense volume of oil in the un- 
 derlying sands. The deepest formation in this region that now seems 
 worth testing is estimated to lie 4,000 or 5,000 feet below the surface and 
 may be below profitable drilling depth. This formation is the Trinity, which 
 in Pike and Sevier counties, Arkansas, contains asphalt deposits that rep- 
 resent the meager remains of what were once rather large bodies of oil. 
 
 Although the character of the formations in southern Arkansas may 
 require the use of the rotary drill, operators should realize its shortcomings 
 and employ methods that will insure, so far as possible, detection of show- 
 ings of oil and gas. Cores should be cut from all beds penetrated that 
 yield showings, and particularly from a sand near the base of the Midway 
 formation and from sands in the Nacatoch, Marlbrook, Brownstown, Blos- 
 som, Eagle Ford, Woodbine, and Trinity formations, whether or not oil 
 showings are observed in the sludge. 
 
 The ages, relative positions, and thicknesses of the formations encoun- 
 tered in drilling in south-central Arkansas must be determined if the search 
 for oil is to be carried out effectively and economically. These determina- 
 tions are difficult because of the similarity of the beds of the several for- 
 mations, and can be made precise only with the aid of fossils. The ap- 
 proximate boundaries of the larger units, however, may be determined from 
 the character of the beds as shown by well records. The following descrip- 
 tions of formations encountered by drillers in Union County, Arkansas, are 
 the result of a detailed study of many well records by W. W. Rubey, of the 
 U. S. Geological Survey, Department of the Interior. Inaccuracies in the 
 well records may have caused like inaccuracies in the interpretation of the 
 stratigraphy. 
 
 Probably all the rocks that cover the surface of Union County belong 
 to the Claiborne group of the Eocene series of the Tertiary system, which 
 in this general region is divided into two formations, the Yegua above and 
 the St. Maurice below. 
 
 Yegua (?) Formation: 
 
 Recent determinations of fossil plants by E. W. Berry indicate that the 
 Yegua (?) formation is probably present in Union County, and that it com- 
 prises the surface beds over most of the county. The beds that are prob- 
 ably to be assigned to the Yegua ("Cockfield") formation are recorded in 
 well records as alternating layers of sand and gumbo, some shale and cal- 
 careous material ("boulders" and "rocks"), and a little lignite. They may 
 "be distinguished from the underlying beds by their dominant sandiness. 
 These beds probably attain a maximum of slightly more than 450 feet in 
 the southeastern part of the county. 
 
 St. Maurice Formation: 
 
 The strata in this area which are here identified as the St. Maurice for- 
 mation are commonly recorded in drillers' logs as layers of shale and 
 gumbo with many "boulders" and "rocks" and some sandy material. The 
 St. Maurice is much freer from sand than the formations above and below 
 it. It probably ranges in thickness from 90 feet in the northwest corner of 
 the county to about 200 feet in the southeastern part' .
 
 EL DORADO, ARK., OIL AND GAS FIELD 
 
 Wilcox Formation: 
 
 The Wilcox formation is generally shown in logs as thick alternating 
 layers of sand, sandy gumbo, and shale, with some zones marked by "rocks" 
 and "boulders," although subordinate amounts of gravel and lignite are oc- 
 casionally noted. This formation can be recognized by an upper sandy 
 group and a lower shaly group which contain less sand. Its thickness 
 averages about 600 feet throughout Union County, but increases slightly 
 toward the east. 
 
 Formations similar in composition to the Wilcox have yielded small 
 quantities of oil in Louisiana and Texas, and the expectation that some oil 
 may be obtained from this formation in restricted areas is not unreasonable. 
 A careful watch should therefore be kept for indications of oil or gas 
 while wells are penetrating these beds. 
 
 Midway Formation: 
 
 The beds referred to as the Midway formation are recorded by the 
 drillers as "boulders," "rocks," and layers of sand, gumbo, and shale, with 
 more or less chalk, limestone, and gypsum. Recent microscopic studies of 
 cuttings from wells in the El Dorado field by James Gilluly, of the U. S. 
 Geological Survey, have shown these beds to include some lignite. This 
 occurrence of carbonaceous material in .the Midway, although by no means 
 widespread, is nevertheless not unusual. This formation is characterized 
 throughout by its relative hardness. 
 
 The greatest known thickness of the Midway at its outcrop is about 260 
 feet* but this measurement was taken near the shore line of the embayment 
 in which the formation was deposited. The character of the strata pene- 
 trated indicates that the formation probably attains a maximum thickness 
 of slightly more than 500 feet in Union County. 
 
 Many wells drilled in south-central Arkansas have obtained showings 
 of oil or gas or flows of water in a sandy bed near the base of this forma- 
 tion. At only a few wells, however, have tests been made to ascertain the 
 true value of these showings. Especially in the El Dorado field has this 
 bed remained untested. 
 
 Arkadelphia Clay: 
 
 The Arkadelphia clay of the Upper Cretaceous or Gulf series is in gen- 
 eral easily recognized by its thickness and its freedom from sand. The 
 strata recorded are mainly shale and gumbo, which are generally accom- 
 panied by many layers of "boulders,"' "rocks." chalk, limestone, and gyp- 
 sum, and in a few wells layers of sandy shale. A very noticeable group of 
 chalky or calcareous beds makes up the lower 175 or 200 feet of the Arka- 
 delphia. The thickness of this formation averages about 550 feet in the 
 western part of Union County and increases eastward, possibly to as much 
 as 600 feet near the eastern boundary. 
 
 Nacatoch Sand: 
 
 The drillers' logs record the Nacatoch sand as beds of hard sand, shale, 
 and limestone with may layers of "rocks," ''boulders," and "pyrite" and 
 some gumbo and chalky material. The upper part is commonly hard and 
 sandy; the lower varies from slightly calcareous shale to hard limestone, 
 although it usually includes thin sandy layers. The thickness ranges from 
 150 to 200 feet. 
 
 The Nacatoch has been identified by its fossils as the producing sand 
 at El Dorado. t The oil there is obtained from three or four discontinuous 
 layers of sandstone in the upper fifty feet of the formation. 
 
 Marlbrook Marl: 
 
 The Marlbrook marl is recorded as shale, chalk, "boulders," limestone, 
 and lesser amounts of gumbo, "rocks," and "pyrite," and some sandy shale. 
 This formation consists typically of shale and varying amounts of calca- 
 reous material. It ranges in thickness from about 300 to nearly 350 feet. 
 
 ft/. 5". GeoL Survey Press Notice: Oil from the Nacatoch Sand, El Dorado, 
 Ark., Feb. 7, 1922. 
 
 *Kennedy, William. A section from Terrell, Kaufman County, to Sabine Pass 
 on the Gulf of Mexico: Texas Geol. Survey, Third Annual Report, p. 49, 1892.
 
 EL DORADO, ARK., OIL AND GAS FIELD 81 
 
 A group of sandy shales between 400 and 500 feet below the top of the 
 Xacatoch usually yields water wherever it is penetrated. The beds at this 
 horizon may contain oil or gas where the structure is favorable. 
 
 Annona Tongue of the Austin Chalk (?): 
 
 Fossils obtained from one of the wellst indicate the Marlbrook age of 
 strata at least 250 feet below the base of the Nacatoch sand, and as no 
 marked change in the character of the sediments down to the Brownstown 
 marl is recorded, the Annona tongue of Austin chalk may be absent here. 
 However, as this tongue, in its area of outcrop, varies from typical chalks 
 to calcareous clays, it is probably present in Union County, but because of 
 this lithologic variation it may not be easily distinguished from the over- 
 lying Marlbrook marl. The boundary between the Marlbrook marl and the 
 Annona tongue of the Austin is provisionally drawn at the upper surface 
 of a persistent limy or chalky series. As thus identified the Annona tongue 
 in Union County consists of strata recorded in logs as limy shale, gypsum, 
 and gumbo, with some "rocks," sandy shale, or chalk; its thickness ranges 
 from 60 to 100 feet . 
 
 Brownstown Marl: 
 
 The strata referred to the Brownstown marl are dominantly calcareous 
 sandy shales. They are usually called sandy shale, hard shale, "rock," 
 sand, and gumbo in drillers' logs. Subordinate amounts of lime stone, 
 "boulders," "pyrite," gypsum, and chalk are frequently noted. The thick- 
 ness of the Brownstown ranges from about 200 to nearly 300 feet and ap- 
 parently increases westward. 
 
 The formation is unique among those penetrated in that its thickness 
 seems to decrease eastward across Union County. This fact is doubtless 
 associated with a marked increase in sandiness of the Brownstown from 
 its outcrop in Hempstead County southeastward through Union County. 
 Any conclusions as to the cause of these changes would be unwarranted if 
 based entirely on evidence furnished by records of rotary-drilled wells, but 
 the presence of these sandy layers may well justify a thorough test of this 
 formation. 
 
 Blossom (?) Sand: 
 
 A group of beds below the Brownstown marl, consisting of about 65 feet 
 of sandstone, shale, and some calcareous layers, is probably to be correlated 
 with the upper part of the Bingen formation of southwestern Arkansas and 
 is therefore tentatively referred to as the Blossom sand. The Bingen for- 
 mation is considered by L. W. Stephenson "as the probable near-shore equiv 
 alent of the Blossom sand, the Eagle Ford clay, and part of the Woodbine 
 sand, but these formations are probably represented in part by unconfor- 
 mities within the Bingen and at its base. Indeed, it is possible that the 
 Woodbine sand is entirely represented by the unconformity at the base of 
 the Bingen." Sandy layers in the upper part of the Blossom (?) sand com- 
 monly carry water and are thought to correspond to the oil sand or sands 
 in the Haynesville field, in Louisiana, although the formations there have 
 not been positively identified. The Blossom (?) sand lies from 800 to 850 
 feet below the top of the Nacatoch sand over most of Union County and 
 probably about 810 to 830 feet in the productive part of the El Dorado field. 
 
 Eagle Ford (?) Clay: 
 
 The several hundred feet of calcareous or limy shales below the 
 Blossom (?) sand that have been penetrated in Union County probably be- 
 long to the Eagle Ford ( ?) clay of Upper Cretaceous age. In the logs of 
 some wells in and near Union County a few red layers are recorded from 
 these shales (see the accompanying cross section), and in parts of the 
 Bingen formation of southwestern Arkansas that are presumably to be corre- 
 lated with the true Eagle Ford clay much reddish material has been noted, 
 both at the outcrop* and in wells. t 
 
 *Miscr. H. D.. and Purdue. A. H.. Grarcl Deposits of the Caddo Gap and 
 PC Queen Quadrangles, Ark.: U. S. Gcol. Survey Bull. 690, />/>. 22-24, 1919. 
 
 IMiser, H. D., and Purdue, A. H., Asphalt Deposits and Oil Conditions in 
 Southwestern Ark.: U. S. Geol. Survey Bull. 691, Pt>. 282-291, IQIQ. 
 
 tL'. 5. Geol. Survey Press Notice: Oil from the Nacatoch Sand, El Doradc. 
 Ark., Feb. 7, 1922.
 
 82 EL DORADO, ARK., OIL AND GAS FIELD 
 
 The principal oil sands of the Caddo and DeSoto-Red River districts, in 
 Louisiana (which are commonly but erroneously called the Woodbine sand), 
 are probably of Eagle Ford age.fl The horizon of these oil-bearing strata 
 in Louisiana is estimated to lie 500 feet more or less, below the top of the 
 Blossom (?) sand in Union County, Ark., and from about 1,300 to 1.400 feet 
 below the upper surface of the Nacatoch. So far as known, this horizon 
 has not been reached in Union County. 
 
 RECORD OF DEEP WELL NEAR EL DORADO 
 
 Detailed information regarding the nature of the beds penetrated may 
 be obtained from the following record of one of the deepest wells in Union 
 County, Hammond well No. 1 of Cooper & Henderson Oil Company, in SEV4 
 SW%, Sec. 19, T. 17 S.. R. 15W.: 
 
 (Elevation above sea level about 204 feet. Geologic correlations by 
 U. S. Geological Survey. All tormational boundaries are fixed tentatively 
 except that between the Arkadelphia and. Nacatoch.) 
 
 Material Thickness Depth 
 
 Eocene series: 
 Claiborne group: 
 
 Yegua (?) formation: 
 
 Surface sand 30 30 
 
 Sand 20 50 
 
 Gumbo 11 61 
 
 Packed sand 6 67 
 
 Rock 3 70 
 
 Packed sand 40 110 
 
 Hard sand 45 155 
 
 Rock 2 157 
 
 Hard sand 20 177 
 
 Gumbo; set 12%-inch casing 4 181 
 
 Gumbo 6 187 
 
 Sand and boulders... , 6 193 
 
 Packed sand and boulders : 20 213 
 
 Gumbo 25 238 
 
 Rock and sand 2 240 
 
 Packed sand 10 259 
 
 Sandrock 5 2o5 
 
 Sand and boulders 3 258 
 
 Sand boulders and gumbo 100 358 
 
 St. Maurice formation (position of contact doubtful; 
 
 lies above in the 100 feet of sand, boulders and 
 
 gumbo) : 
 
 Sand and boulders 18 376 
 
 Rock 2 378 
 
 Packed sand 9.... 387 
 
 Rock 3 390 
 
 Gumbo 10 400 
 
 Sand and gumbo 20 420 
 
 Gumbo 22 442 
 
 462 
 504 
 
 518 : 
 
 536 
 
 679 . 
 
 702 . 
 
 708. 
 
 751 
 
 805 
 813 
 
 Wilcox formation: 
 Boulders 
 Boulders 
 Sand and boulders 
 Packed sand 
 
 20 
 
 I 14 
 18 
 36 
 
 
 107 
 
 Sand and boulders : 
 Gumbo 
 Sand and boulders 
 Gumbo 
 Gumbo 
 Gumbo and boulders 
 
 23 
 6 
 43 
 26 
 28 
 8
 
 _ EL DORADO, ARK., OIL AND GAS FIELD 
 
 Rock 4 817 
 
 Gumbo 7 824 
 
 Gumbo 41 865 
 
 Rock 3 868 
 
 Gumbo and boulders 8 876 
 
 Gumbo and -boulders 30 906 
 
 Gumbo 5 911 
 
 Gumbo and boulders 42 953 
 
 Packed sand 10 963 
 
 Broken sandrock 6 969 
 
 Gumbo 20 . 989 
 
 Sand 16 1,005 
 
 Sandrock 19 1,024 
 
 Midway formation: 
 
 Hard sand 6 1,030 
 
 Gumbo 6 1.036 
 
 Gummy shale , 20 1,056 
 
 Sand and boulders 27 1,083 
 
 Gumbo 15 1,098 
 
 Sand and. sandrock 7 1,105 
 
 Broken formation 23 1,128 
 
 Broken formation 13 1,141 
 
 Sandy gumbo : 15 1,156 
 
 Gumbo 71 1,227 
 
 Shale : 12 1,239 
 
 Sand and boulders.. 11 1,250 
 
 Gumbo 20 1,270 
 
 Gumbo 14 1,284 
 
 Rock 1 1,285 
 
 Rock 2 1,287 
 
 Gumbo 14 1,301 
 
 Lignite 5 1,306 
 
 Gumbo 14 1 ,320 
 
 Gumbo 20 1,340 
 
 Rock 1 1,341 
 
 Sand 12 1,353 
 
 Sand and boulders 8 1,361 
 
 Gypsum 31 1,392 
 
 Gumbo 8 1,400 
 
 Gumbo : 86 1,486 
 
 Gumbo 25 1,511 
 
 Rock ' 3 1,514 
 
 Rock 3 1,517 
 
 Upper Cretaceous or Gulf series: 
 
 Arkadelphia Clay: 
 
 Gumbo 10 1,527 
 
 Gumbo 23 1,550 
 
 Hard shale 5 1,555 
 
 Gumbo 8 1,563 
 
 Gumbo 1 2 1.575 
 
 Gumbo 20 1,595 
 
 Shale . 5 1,600 
 
 Gumbo 30 1,630 
 
 Gummy shale 4 1,634 
 
 Gummy shale 60 1,694 
 
 Gumbo 52 1,746 
 
 Shale and gumbo 65 1,811 
 
 Shale and boulders 10 1,821 
 
 Shale - 23 1,844 
 
 Gummy shale 18 1,862 
 
 Shale and gumbo 30 1,892 
 
 Gumbo 27 1,919 
 
 Gypsum 10 1.929 
 
 Hard shale : 20 1.949 
 
 Gumbo - . 27 1.976 
 
 Gumbo and shale 44 2.020 
 
 Hard shale and gumbo; set S^-inch casing 25 2,045 
 
 Gumbo : 5 2,050
 
 EL DORADO, ARK., OIL AND GAS FIELD 
 
 Gumbo and shale 
 
 Gumbo and shale 
 
 Shale and gumbo 
 Nacatoch sand: 
 
 Hard lime and shale 
 
 Gumbo 
 
 broken rock 
 
 Sand ................................... - 
 
 Sand 
 
 Broken rock 
 
 Sand ..... : 
 
 Sand 
 
 Rock 
 
 Sand 
 
 Sand 
 
 Shale and boulders 
 
 Gumbo 
 
 Gummy shale 
 
 Shale and gumbo 
 
 Gummy shale ............................ . 
 
 Shale and lime ..... 
 Marlbrook marl: 
 
 Shale and boulders 
 
 Gummy shale 
 
 Shale and boulders 
 
 Hard shale 
 
 Hard shale 
 
 Salt-water sand 
 
 Rock 
 .Sandrock 
 
 Sandrock 
 
 Sandy shale 
 
 Gummy shale 
 
 Rock 
 
 Gummy shale 
 
 Shale 
 
 *Sandy shale 
 . Hard shale ......................... ... 
 
 Rock 
 
 Gumbo 
 
 Gumbo 
 
 Gumbo 
 
 Gumbo ...... 
 
 Hard shale ............................. 
 
 Annona tongue of Austin chalk 
 
 Broken sandrock 
 
 Broken sandrock 
 
 Hard shale 
 
 Gumbo 
 
 Gumbo 
 
 Hard sand 
 
 nock 
 
 Gumbo 
 
 Lime and shale 
 
 Rock 
 
 Lime and shale 
 Brownstown marl: 
 
 Gumbo 
 
 Rock 
 
 Gumbo 
 
 Gumbo 
 
 Hard sandy shale 
 
 Gumbo 
 
 Gumbo 
 
 Sand, showing salt water 
 
 Gumbo 
 
 Hard gummy shale 
 
 Rock 
 
 24 
 ....... 48 
 
 26 
 14 
 
 45 
 41 
 14 
 95 
 15 
 
 2,082 
 2,J96 
 2,111 
 
 2,117 
 2,137 
 2,140 
 2,146 
 2,148 
 2,150 
 2,156 
 2,160 
 2,164 
 2,166 
 2,170 
 2,184 
 2,189 
 2,213 
 2,261 
 2,287 
 2,301 
 
 2,346 
 2,387 
 2,401 
 2,496 
 2,511 
 2,519 
 2,521 
 2,523 
 2,528 
 2,530 
 2,535 
 2,537 
 2,544 
 2,548 
 2,552 
 2,565 
 2,567 
 2,579 
 2,594 
 2,604 
 2,624 
 2,629 
 
 2,633 
 2,637 
 2,650 
 2,653 
 2,662 
 2,665 
 2,669 
 2,675 
 2,700 
 2,702 
 2,727 
 
 2,734 
 2,740 
 2,741 
 2,755 
 2,765 
 2,770 
 2,774 
 2,780 
 2,792 
 2,814 
 2,822
 
 EL DORADO, ARK., OIL AND GAS FIELD 85 
 
 Rock .. . 2,825 
 
 Rock 5 2,830 
 
 Hard sandy shale 26 2,856 
 
 Hard sandy shale 21 2,877 
 
 Gumbo 5 2,882 
 
 Hard shale 3 2,885 
 
 Hard shale 9 2,894 
 
 Rock 1 2,895 
 
 Rock '. 3 2,898 
 
 Shale 3 2,901 
 
 Shale and gumbo 5 2,906 
 
 Hard sandy chalk 4 2,910 
 
 Sandy chalk ... 14 2,924 
 
 Hard shale -'.- ... 15 2,939 
 
 Blossom (?) sand: 
 
 Sand 2 2,941 
 
 Sand 14 2,955 
 
 Rock 3 2,958 
 
 Sand 2 2,960 
 
 Sandrock .1 2 2,962 
 
 Gumbo 20 2,982 
 
 Sandy shale 8 2,990 
 
 Shale and boulders 1 2,991 
 
 Rock 1 2,992 
 
 Sand 6 2,998 
 
 Sand and gravel 7 3,005 
 
 Eagle Ford (?) clay: 
 
 Gumbo 14 3,019 
 
 Gummy shale 7 3,026 
 
 Gumbo 22 3,048 
 
 Gummy shale ! 9 3,057 
 
 Broken limerock 28 3,085 
 
 Shale 7 3,092 
 
 Broken limerock and shale 22 3,114 
 
 Shale 6 3,120 
 
 Broken limerock 20 3,140 
 
 Shale 6 3,146 
 
 Broken limerock and shale 17 3,163 
 
 Broken lime and shale 37 3.200 
 
 Geologic Structure in the Region: 
 
 The accompanying cross section, from the vicinity of Centerpoint, 
 Howard County, Ark., in the Caddo Gap quadrangle, to a point about ten 
 miles east of El Dorado, Union County, shows the general structural con- 
 ditions in south central Arkansas. The diminishing slope and the general 
 increase of thickness of the formations as the center of the embayment 
 is approached is readily apparent. 
 
 The elevation of the surface as shown is based on a partial revision of 
 a map previously published by the Survey*, and is included in this dia- 
 gram to show the relation of outcrops to formation below the surface and 
 the depth of the oil and gas bearing sands. Topographic details near the 
 wells are necessarily obscured because of the exaggerated width of the 
 graphic logs. The records of the Nashville, Hope, and Bodcaw wells with 
 correlations? and the outcrops of the formations}! were taken from pub- 
 lished reports. 
 
 * Harris, G. D., Oil and Gas in Louisiana: V. S. Gcol. Surrey Bulletin 429, 
 pi. 12. 1910. 
 
 *A small fossil obtained from this depth indicates that these beds are no 
 older than the Marlfronk marl. U. S. Geol. Survev Press Notice: Oil from 
 the Nacatoch Sand, El Dorado. Ark., Feb. ~, 1922.
 
 M-; EL DORADO, ARK., OIL AND GAS FIELD 
 
 The strata recorded in a number of the available logs of wells drilled 
 in and near Union County were also correlated and the results are given in 
 the descriptions of the formations. Maps showing the structure of the 
 Xacatoch and other formations in south central Arkansas have been pre- 
 pared bv Veatch. A general structural contour map of Union County 
 has not been made, as a sufficient number of well logs for that purpose has. 
 not been obtained, but the position relative to sea level of the upper sur- 
 face of the Nacatoch sand and other interesting features of the wells studied 
 are given in the following tabulation. 
 
 +Miser, H. D., and Purdue, A. H., Asfhalt Deposits and Oil Conditions in 
 
 Southwestern Arkansas: U. S. Gcol. Surrey Bulletin 6yi, />/>. 2X2-2^2. />/. .?j, /y/v. 
 
 ^Harris, G. D., Oil and Gas in Louisiana: U. S. Gcol. Survey Bulletin .}_>,. 
 
 />/. 12; 1910. 
 
 ]~eatch, A. C., Geology and Underground H'atcr Resources of Xortlieni 
 Louisiana and Southern Arkansas: U. S. Gcol. Surrey Prof. Paper 46. mnf).
 
 PART III 
 
 New Wells Show Extension 
 of El Dorado Field 
 
 On the eve of going to press with the final forms of this report, infor- 
 mation was received by the department of the bringing in of several new 
 wells, indicating a considerable extension of the El Dorado Field, espe- 
 cially in a north and east direction. Mr. J. A. Brake, State Oil and Gas 
 Inspector, El Dorado, Ark., has kindly furnished the department with logs 
 and photographs of these new wells, and this information is supplemented 
 to that which had already been prepared by the authors of this report, with 
 the explanation that there was no opportunity for these authors to make 
 comment upon the new wells or the bearing of these important discoveries 
 upon future developments in the field. Mr. Brake says: "The new wells 
 are a revelation. The log of the deep sand, which shows the new field, and 
 the log of the north field, which shows still another formation, I think art- 
 better than any we have yet found." 
 
 East Field Four Miles East of El Dorado. 
 
 Six big gas wells have been brought in in the East Field, two of them 
 making 45,000,000 cubic feet each with a rock pressure of 1.050 pounds. The 
 other four wells are two and one-half miles farther north and they are mak- 
 ing 20,000.000 cubic feet with a rock pressure of 850 pounds. 
 
 Four oil wells have been brought in in this same territory, one of them 
 making 2,000 barrels and still is producing at The rate of 1,200 barrels. 
 About twenty wells are now being drilled in this east field. 
 
 North Field, Eight Miles North of El Dorado. 
 
 Murphy No. 1. in 8-16-13, shows a different log, with much more shale, 
 than any of the other wells, and the sand is found 176 feet higher than in 
 the old field of Union county. 
 
 Log of Murphy No. 1 the Wild Well 
 Elevation 218 feet. Location SYV Corner 01 NE^i of SE*4: 
 
 'I lo 25. sand 1163. gumbo 
 
 183, sand and clay (set 10-in. 1165. rock 
 
 casing 116 f. gumbo 
 
 190, gumbo 12oo. gumbo 
 
 I'.".:., sand and shale 1229. shale \ 
 
 288, gumbo and boulders 1232, rock 
 
 ::<HI. boulders ' 1269, tough blue gumbo 
 
 M33. sand and shale 1309, gumbo, blue 
 
 IT.'i, shale and gumbo 1445, gumbo, blue 
 
 500, hard sand 1490, gumbo, black 
 
 608, gumbo and boulders 1581, gumbo and shale, black 
 
 <i.~jl. gumbo lfii.ui. gumbo, black 
 
 <!52. rock 1668, black shale and boulders 
 
 TIKI, shale and gumbo 1728. shale and boulders 
 
 746. gumbo and boulders 1740. gumbo, black 
 
 748, rock 1760. shale, black 
 
 788. black shale 1781. gumbo 
 
 S12. gumbo and boulders. 1795, gumbo, black 
 
 895. shale, black 1805, shale 
 
 *J60 gumbo and boulders 1841, gumbo and boulders 
 
 !K!6. packed sand and boulders 1865, gumbo 
 
 1060. sticky shale 1909, gumbo, black 
 
 1 <5i. rock 1960, gumbo and shale 
 
 1062, rock 1975, gumbo 
 
 ,./o". snaif. black 2000, shale 
 
 1081. rock 2'! 12. gumbo 
 
 iti82. rock 2023. shale 
 
 I 140. L -unibo 2024. sand 
 
 II "10. sand, lignite and boulder d
 
 *8 EL DORADO. ARK., OIL AND GAS FIELD 
 
 Photo by Taylor 
 Burning Well by Day Murphy No. 1, Sec. 8-16-15
 
 EL, DORADO, ARK., OIL AND GAS FIELD 
 
 89 
 
 West Field, Three Miles West of El Dorado. 
 
 On May 7, 1922, the El Dorado Natural Gas & Petroleum Corporation 
 brought in a well on the Frazier lease in 1-18-16, making 4,000,000 feet of 
 dry gas. After blowing for a short time it increased to 45,000,000 and blew 
 off all the fittings and went wild. The first day after being wild it com- 
 menced making oil. This well came from the deep, or new, sand at 2,529 
 feet. The well was successfully capped and closed in and was at that time 
 making 50,000,000 feet of gas and 300 barrels of oil.. Three or four deep 
 test wells are being drilled in the field at this time. 
 
 Log of Frazier Well 
 
 
 
 to 
 
 6, 
 
 surface sand 
 
 1285 
 
 to 
 
 1330, 
 
 sand 
 
 G 
 
 to 
 
 12, 
 
 sand and gravel 
 
 1330 
 
 to 
 
 1340, 
 
 shale . 
 
 12 
 
 to 
 
 65, 
 
 clay. 
 
 1340 
 
 to 
 
 1344, 
 
 sand 
 
 65 
 
 to 
 
 160, 
 
 sand clay 
 
 1344 
 
 to 
 
 1355, 
 
 shale and sand 
 
 160 
 
 to 
 
 175, 
 
 sand 
 
 1355 
 1375 
 
 to 
 
 to 
 
 1375, 
 1408 
 
 gumbo 
 
 
 
 
 ing 
 
 1408 
 
 to 
 
 1412! 
 
 gumbo 
 
 185 
 
 to 
 
 190, 
 
 sand 
 
 1412 
 
 to 
 
 1416, 
 
 rock 
 
 190 
 
 to 
 
 
 sand with clay and lime 
 
 1416 
 
 to 
 
 1455, 
 
 sand 
 
 
 
 
 chalk 
 
 1455 
 
 to 
 
 1465, 
 
 shale 
 
 225 
 
 to 
 
 235, 
 
 gumbo 
 
 1465 
 
 to 
 
 1470, 
 
 rock 
 
 235 
 
 to 
 
 265, 
 
 sand 
 
 1470 
 
 to 
 
 1474, 
 
 sand 
 
 265 
 
 to 
 
 285, 
 
 shale 
 
 1474 
 
 to 
 
 1495, 
 
 jipsy chalk 
 
 285 
 
 to 
 
 300, 
 
 gumbo 
 
 1495 
 
 to 
 
 1498, 
 
 gumbo 
 
 300 
 
 to 
 
 335, 
 
 sand 
 
 1498 
 
 to 
 
 1530, 
 
 rock 
 
 335 
 
 to 
 
 355, 
 
 white sand 
 
 1530 
 
 to 
 
 1570, 
 
 sand 
 
 355 
 
 to 
 
 380, 
 
 gumbo 
 
 1570 
 
 to 
 
 1580, 
 
 gumbo 
 
 380 
 
 to 
 
 395, 
 
 sand 
 
 1580 
 
 to 
 
 1665, 
 
 shale 
 
 395 
 
 to 
 
 415, 
 
 shale 
 
 1665 
 
 to 
 
 1705, 
 
 gumbo and sand 
 
 415 
 
 to 
 
 435, 
 
 gumbo 
 
 1705 
 
 to 
 
 1735, 
 
 rock 
 
 435 
 
 to 
 
 445, 
 
 clay 
 
 1735 
 
 to 
 
 1885, 
 
 sand 
 
 445 
 
 to 
 
 500, 
 
 gumbo 
 
 1885 
 
 to 
 
 1920, 
 
 gumbo 
 
 500 
 
 to 
 
 525, 
 
 sand 
 
 1920 
 
 to 
 
 2005, 
 
 shale 
 
 525 
 
 to 
 
 555, 
 
 gumbo, brown 
 
 2005 
 
 to 
 
 2025, 
 
 rock 
 
 555 
 
 to 
 
 580, 
 
 rock 
 
 2025 
 
 to 
 
 2035, 
 
 sand 
 
 580 
 
 to 
 
 635, 
 
 gumbo 
 
 2035 
 
 to 
 
 2040, 
 
 gumbo 
 
 635 
 
 to 
 
 655, 
 
 sand 
 
 2040 
 
 to 
 
 2050, 
 
 shale 
 
 655 
 
 to 
 
 665, 
 
 gumbo 
 
 2050 
 
 to 
 
 2080, 
 
 boulders 
 
 665 
 
 to 
 
 730, 
 
 clay 
 
 2080 
 
 to 
 
 2105, 
 
 gummy shale 
 
 730 
 
 to 
 
 760, 
 
 loose and gumbo 
 
 2105 
 
 to 
 
 2125, 
 
 gumbo 
 
 760, 
 
 to 
 
 775, 
 
 sand and gumbo 
 
 2125 
 
 to 
 
 2155, 
 
 hard shale 
 
 775 
 
 to 
 
 785, 
 
 gumbo 
 
 2155 
 
 to 
 
 2160, 
 
 sand, shale 
 
 785 
 
 to 
 
 815, 
 
 sand 
 
 2160 
 
 to 
 
 2165, 
 
 gumbo 2165 8-inch 
 
 815 
 
 to 
 
 825, 
 
 clay 
 
 
 
 
 casing 
 
 825 
 
 to 
 
 860, 
 
 gumbo 
 
 2165 
 
 to 
 
 2365, 
 
 broken sand and shale, 
 
 860 
 
 to 
 
 885, 
 
 sand 
 
 
 
 
 showing little gas 
 
 885 
 
 to 
 
 960, 
 
 shale 
 
 
 
 2365, 
 
 500 feet of oil stand in 
 
 960 
 
 to 
 
 965, 
 
 rock 
 
 
 
 
 hole. Well bailed dry. 
 
 965 
 
 to 
 
 970, 
 
 gumbo 
 
 
 
 
 Drilling commenced at 
 
 970 
 
 to 
 
 980, 
 
 sand 
 
 
 
 
 2377 sand 
 
 980 
 
 to 
 
 985, 
 
 rock 
 
 2365 
 
 to 
 
 2377, 
 
 sand 
 
 985 
 
 to 
 
 990, 
 
 lime rock 
 
 2377 
 
 to 
 
 2425, 
 
 sand and shale 
 
 990 
 
 to 
 
 1000, 
 
 gumbo 
 
 2425 
 
 to 
 
 2440, 
 
 gumbo 
 
 1000 
 
 to 
 
 1035, 
 
 shale 
 
 2440 
 
 to 
 
 2462, 
 
 shale and gumbo (most 
 
 1035 
 
 to 
 
 1038, 
 
 rock 
 
 
 
 
 shale) 
 
 1038 
 
 to 
 
 1055, 
 
 gumbo 
 
 2462 
 
 to 
 
 2470, 
 
 shale 
 
 1055 
 
 to 
 
 1090, 
 
 shale and boulders 
 
 2470 
 
 to 
 
 2475, 
 
 hard sand 
 
 1090 
 
 to 
 
 1105, 
 
 sand 
 
 2475 
 
 to 
 
 2498, 
 
 gumbo 
 
 1105 
 
 to 
 
 1120, 
 
 gumbo 
 
 2498 
 
 to 
 
 2506, 
 
 gumbo and lime 
 
 1120 
 1160 
 
 to 
 
 to 
 
 1160, 
 1175, 
 
 shale 
 gumbo and boulders 
 
 !. r )06 
 
 to 
 to 
 
 2524, 
 2529, 
 
 tough gumbo 
 soft shale 
 
 1175 
 
 to 
 
 1195, 
 
 shale 
 
 
 
 2529, 
 
 Hard gas rock and 2-in 
 
 1195 
 
 to 
 
 1198, 
 
 rock 
 
 
 
 
 core taken; 5 3-16 liner 
 
 1198 
 
 to 
 
 1235, 
 
 shale and boulders 
 
 
 
 
 was set. Well came in 
 
 1235 
 
 to 
 
 1238, 
 
 sand with streaks of 
 
 
 
 
 making dry gas after 
 
 
 
 
 gumbo 
 
 
 
 
 bailing 
 
 1238 
 
 to 
 
 1285, 
 
 gumbo 
 
 
 
 
 
 South Field, Nine Miles South of El Dorado. 
 
 They are still bringing in 1,000-barrel wells in the south field, and there 
 is quite a good deal of activity there at present. Much of the oil in the 
 south field runs 42 and 43 gravity. This oil commands a premium. 
 
 There is being produced at the present time about 40,000 barrels of oil 
 per day at a price ranging from $1.75 to $2.00 and $2.10 per barrel.
 
 EL DORADO, ARK., OIL AND GAS FIELD 
 
 Photo by Taylor 
 Burning Well by Night "Arkansas Lighting the World"
 
 INDEX 
 
 A 
 
 Page 
 
 Acknowledgments 7 
 
 Acreage and Oil Prices 11 
 
 Air Lifts for Raising Oil 66 
 
 Annona Tongue, Austin Chalk (?) 81 
 
 Arkadelphia Clay 80 
 
 Association of Oil and Water 33 
 
 Analysis of Underground Waters 31 
 
 B 
 
 Blossom (?) Sand 81 
 
 Bridges and Plugs of Cement or Other Impervious Ma- 
 terial 28 
 
 Brownstown Marl 81 
 
 Bureau of Mines, Co-operation 12 
 
 Busey Well 8 
 
 C 
 
 Casing Programs 14 
 
 Cement, Use of 34 
 
 Chemical Analysis of Water, Comparison 31 
 
 Completing Wells 18 
 
 Conclusion 68 
 
 Constantin Well 8 
 
 Conservation, State Commission, Regulations, etc 12 
 
 Counterbalances and Tail Pumps..... 68 
 
 D 
 
 Deeper Production, Protection in Case of 43 
 
 Dehydration of El Dorado Oil , 60 
 
 Drilling Costs 22 
 
 Drilling Methods 13 
 
 Drilling Methods, Some Mistakes 79 
 
 E 
 
 Eagle Ford (?) Clay 81 
 
 Equipment and Power :.. 13 
 
 Evaporation Loss of Crude Oil 48 
 
 F 
 
 Flow Oil Through Tubing 66 
 
 Fluid Levels, Comparisons of 28 
 
 Formation, Production and Casing Records ... 26
 
 G 
 
 Page 
 
 Gasoline from Natural Gas 62 
 
 Gas, Production of 51 
 
 Geologic Structure in the Region 71-85 
 
 Geologic Structure, Relation of Sequence of Wells 
 
 "Going to Water" 30 
 
 Geology, Studies of the Field 71 
 
 H 
 History of Development S 
 
 I 
 Introduction 
 
 L 
 Labor Conditions 
 
 M 
 
 Map, Methods Used in Construction of 76 
 
 Marlbrook Marl, Source of Oil 80 
 
 Midway Formation, Showings of Oil and Gas 80 
 
 N 
 
 Nacatoch Sand, Its Part in Production 80 
 
 Nacatoch Sand, Elevations 78 
 
 O 
 
 Oil and Gas Above the Principal "Pay" Sand 75 
 
 Oil, Character of 77 
 
 Oil, Recovery from Unconsolidated Sands 64 
 
 P 
 
 Packers Used in Casing or in Formation 30 
 
 Perforated Liners and Screen Pipe 65 
 
 Physical Characteristics of Water, Comparison 27 
 
 Pool, How It Was Formed 74 
 
 Possible Extensions of the Field 75 
 
 Possibility of Similar Fields Elsewhere in Southern 
 
 Arkansas 75 
 
 Power for Pumping 67 
 
 Producing Bed, Description of 76 
 
 Production Decline Curves for Oil Wells 53 
 
 Production, Estimated Future and Ultimate 53 
 
 Production Methods 55 
 
 Production Records 44 
 
 Proven Acreage 44 
 
 Pumps, Types for Oil Wells 64 
 
 Q 
 
 Quality of Oil ... 48
 
 Page 
 Recommendations 68 
 
 S 
 
 Safety Devices 56 
 
 Saint Maurice Formation 79 
 
 Separations for Oil, Gas and Water 58 
 
 Storage and Marketing Facilities 11 
 
 Structure of the Field 71-85 
 
 Surface Wastage 48 
 
 T 
 
 Testing Formations 14 
 
 Tracing Underground Flow of Water by Use of Dye, etc. 29 
 
 U 
 Underground Waters, Analyses of ; 31 
 
 V 
 Vacuum Pumping 67 
 
 W 
 
 Water, Amounts Produced by Wells 22-27 
 
 Water Conditions 22 
 
 Water, Comparison of Physical Characteristics 27 
 
 Well, Record of Hammond No. 1 82 
 
 Wells, Abandonment of 41 
 
 Well Spacing 44 
 
 Wilcox Formation 80 
 
 Y 
 Yegua (?) Formation ... 79
 
 The RALPH D. REED LIBRARY 
 
 DEPARTMENT OF GEOLOGY 
 
 UNIVERSITY of CALIFORNIA 
 
 LOS ANGELES, CALIF. 
 
 THE LIBRAin 
 
 OflVERSITY O ( i.-M 
 
 L0
 
 MonofocttHid bv 
 : : .j AYLORO iROS. | 
 
 Syr.cus., N. Y. 
 Stockton, CM. 
 
 UCLA-Geology/Geophysics Library 
 
 TN872A72B4 
 
 I III II II I II Illl II I 
 AA 001 289 038 o