URBANA tA ILLINOIS STATE GEOLOGICAL SURVEY 3 3051 00000 0202 STATE OF ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION DIVISION OF THE STATE GEOLOGICAL SURVEY FRANK W. DEWOLF, Chief BULLETIN No. 40 OIL INVESTIGATIONS IN 1917 AND 1918 Petroleum in Illinois in 1917 and 1918 By N. O. Barrett Brown County By Merle L. Nebel Goodhope and La Harpe Quadrangles By Merle L. Nebel Parts of Pike and Adams Gounties By Horace Noble Coryell Experiments in Water Gontrol in the Flat Rock Pool, Crawford County By Fred H. Tough, Samuel H. Williston, and T. E. Savage In Cooperation with the U. S. Bureau of Mines PRINTED BY AUTHORITY OK THE STATE OK ILLINOIS URBANA, ILLINOIS 19 19 Schnepp & Barnes, Printers Springfield, III. 1919. 21856— 3M STATE OF ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION DIVISION OF THE STATE GEOLOGICAL SURVEY FRANK W. DeWOLF, Chief Committee of the Board of Natural Resources and Conservation Feancis W. Shepabdson, Chairman Director of Registration and Education Kendeic C. Babcock Representing the President of the Uni- versity of Illinois Rollin D. Salisbuby Geologist LETTER OF TRANSMITTAL State Geological Survey, Urbana, June 26, 1919. Francis W . Shepardson, Chairman, and Members of the Board of Natural Resources and Conservation, Gentlemen : I submit herewith reports on oil investigations in Illinois in 1917 and 1918, and recommend their publication as Bulletin 40. Although oil production in Illinois continues to be second only to that of coal, the fields are nevertheless on the decline. The situation may be met in two ways — discovery of new fields and improvement of methods of oil extraction. The papers on Pike, Brown and Adams counties and the Goodhope and La Harpe quadrangles are contributions along the first line, pointing out areas of favorable structure that merit testing for oil. The final paper describes methods of water control which will help to prolong the life of existing fields and at the same time, it is believed, reduce the cost of extraction. The discovery of new fields involves considerable uncertainty and risk of capital, as it is impossible to predict the presence of oil in ad- vance; but improvement in methods of well procedure can be confidently expected to react to the benefit of operators, and therefore attention to such problems as are considered in the water-control report is strongly urged. Very respectfully, Frank W. DeWolf, Chief. Digitized by the Internet Archive in 2012 with funding from University of Illinois Urbana-Champaign http://archive.org/details/oilinvestigation40illi GONTENTS PAGE Petroleum in Illinois in 1917 and 1918, by N. O. Barrett,, 9 Brown County, by Merle L. Nebel .' 21 Goodhope and La Harpe Quadrangles, by Merle L. Nebel . 51 Parts of Pike and Adams Counties, by Horace Noble Coryell 69 Experiments in Water Control in the Flat Rock Pool, Craw- ford County, by Fred H. Tough, Samuel H. Williston, and T. E. Savage 97 MAP OF" ILLINOIS Pig. 1. Map showing areas covered by the reports. PETROLEUM IN ILLINOIS IN 1917 AND 1918 By N. O. Barrett OUTLINE PAGE General review 9 Southeastern Illinois 12 Cumberland, Coles, Clark, Jasper, and Edgar counties. 12 Crawford County 14 Lawrence County 14 Wabash County 14 South-central Illinois 15 Macoupin County 15 Clinton County . 15 Marion County , .......... 15 Western Illinois ... 16 Southern Illinois , 16 Northern Illinois 17 Miscellaneous drilling • • • .- ., 17 Summary tables 18 TABLES 1. Illinois oil production, 1905-1918 10 2. Fluctuation in prices per barrel of Illinois petroleum, 1916, 1917, and 1918 11 3. Monthly record of wells drilled in Illinois in 1917 18 4. Monthly record of wells drilled in Illinois in 1918 19 5. County record of wells drilled in Illinois in 1917 19 6. County record of wells drilled in Illinois in 1918 20 GENERAL REVIEW In spite of a 73 per cent reduction in 1918 in the number of wells drilled as compared with the number for 1916, production declined only 24 per cent. Table 1 shows the annual production and value from 1905 to 1918 inclusive and figure 18 presents the same data graphically for the State as a whole and for the various pools individually. As a result of the enormous increase in Kansas' production in 1917 as well as the actual decline that same year in Illinois production, the latter fell in rank from fourth to fifth among oil-producing states. In (9) 10 OIL INVESTIGATIONS 1918, with further reduction of the Illinois total and a considerable in- crease in Louisiana's production, the State fell still another notch lower so far as quantity was concerned. Evidence of the excellence of Illi- nois oil is found in the fact that in the scale of producing states, Illinois ranked fourth and fifth in value of production during 1917 and 1918 respectively, at the same time that it ranked fifth and sixth in quantity of oil. The years 1917 and 1918 were characterized by record-breaking prices as a result of war conditions, the rise continuing without inter- Table 1. — Illinois oil production, 1905-1918 Year Barrels Value Previous 1905 1906 1907 1908 1909 1910 1911 1912 1913 1914 1915 1916 1917 1918 (preliminary estimate) 6,576 181,084 379,050 281,973 686,238 898,339 143,262 317,038 601,308 893,899 919,749 041,695 714,235 776,860 365,974 116,561 3,274,818 16,432,947 22,649,561 19,788,864 19,669,383 19,734,339 24,332,605 30,971,910 25,426,179 18,655,850 29,237,168 31,358,069 31,230,000 ruption from September 1, 1916 on through to the end of 1918. Changes of prices were infrequent during the latter half of 1917 and all of 1918, as a result of the stabilizing effect of the Fuel Administration upon both production and prices. Table 2 gives the prices per barrel of the two grades of Illinois petroleum for the years 1916, 1917, and. 1918. In 1917 there were but 674 wells completed as compared with 1,469 in 1916, and in 1918 there were only 410 completions. This great de- crease obtained in spite of the considerable increase in price — a factor that usually works towards increasing activity — largely because drillers and capital were attracted to the newly discovered and prolific south- western fields, and partly of course because the more promising unex- plored territory in Illinois is becoming continually smaller. With suc- cessful completion of the war, return to normal conditions is presumed ; indeed, the number of wild cat tests and inside wells contemplated for 1919 is indicative of a general resumption of activity. PETROLEUM IN ILLINOIS IN 1917 AND 1918 11 It is an interesting fact that for the month of February 1918, less completed work was done in the Illinois field than for any previous month since Hoblitzel and Son started development work on Parker Table 2. — Fluctuation in prices per oarrel of Illinois petroleum, 1916. 1917, and 1918 \ 1916 1917 1918 Date Illinois Plymouth Illinois Plymouth Illinois Plymouth January 1 $1.47 $1.33 January 2 $1.72 $1.53 January 3 1.57 January 4 1.63 January 8 1.82 1.73 January 15 1.83 January 21 1.38 January 27 1.62 1.43 January 30 1.87 February 9 $2.22 February 16 1.72 March 6 1.53 March 13 1.58 March 16 1.82 1.68 March 21 $< 2.3: March 28 .... 2.32 April 16 1.92 July 9 .... 2.42 July 28 1.72 1.58 August 1 1.62 1.48 August 3 .... 1.38 August 4 1.52 August 14 1.47 1.18 August 16 2.12 2.03 August 17 1.08 August 28 1.03 September 27 2.13 November 18 1.52 November 30 1.13 December 13 1.57 1.23 December 19 1.62 1.33 December 28 1.43 December 29 1.53 Average 1 $1.64 $1.38 $1,975 $1,934 $2,334 $2,287 12 OIL INVESTIGATIONS prairie between Casey and Westfield, in Clark County on the Young farm back in 1904. The severity of the weather, characteristic of the win- ter of 1918, was the immediate cause of this heavy drop in work, though the general decline in activity was also partly responsible. A feature of the industry in Illinois destined to receive an increasing amount of attention during 1919 is the development and adoption of new and better methods of oil extraction with the idea of prolonging the life of existing fields as well as reducing production costs. The final paper of this bulletin describing the use of mud fluid in water-control work, is a contribution along these lines. In 1917, of the 674 wells completed, 172 or 25.6 per cent were dry, and 8 or 1.2 per cent were gas wells. The remaining 494 wells (73.2 per cent) reported as producers, yielded a new production of 10,140 bar- rels, which amounts to an average initial production of 20.6 barrels per well. In 1918 there were 410 wells drilled, of which 120 or 29.4 per cent were dry, and 14 or 3.4 per cent gas producers. The remaining 276 wells (67.2 per cent) yielded a new production of 5,899 barrels, which amounts to an average initial production of 21.1 barrels. The number of wells abandoned is gradually increasing, 145 in 1916, 202 in 1917, and 214 in 1918 ; but these totals are in every case less than the totals of producers brought in for the year in question, which means of course that the number of producing wells in Illinois is still increasing though the rate of increase is gradually lowering. SOUTHEASTERN ILLINOIS Cumberland, Coles, Clark, Jasper, and Edgar Counties In the shallow-sand field of southeastern Illinois 25.3 per cent or 170 of the State's total of 674 completions were drilled in 1917, and 25.1 per cent or 82 of the total of 410 completions were drilled in 1918. Clark County continued to be by far the most active part of this field with 137 completions and a new production averaging 10.5 barrels in 1917, and 71 completions averaging 7.9 barrels in 1918. A few large producers were brought in, the largest for 1917 being Ohio well No. 106 on the N. and K. Young farm in Parker Township, credited with 100 barrels initial production, and the largest for 1918 being Ohio well No. 1 on the C. B. Lee farm in the same township, yielding 60 barrels. The Stock Yards Oil Company made a deep test in Coles County on the Wm. H. Berkley farm, which was probably in Trenton at a depth of 2,400 feet when it was abandoned as dry. It is believed that the sand penetrated in this well at a depth of 2,228 feet may be the equivalent of PETROLEUM IN ILLINOIS IN 1917 AND 1918 13 the pay sand in the Ohio Oil Company's well No. 29 on the K. and E. Young farm a few miles to the southeast. In 1918, tests near Oakland in Coles County along the northwest extension of the La Salle anticline resulted in two good gas wells. The test put down by the Women's Federal Oil Company in sec. 30 of East Oakland Township on the Sam Daugherty farm in April, 1918, produced 500,000 cubic feet of gas at 302 feet and another on the Hawkins farm, completed in June, produced 700,000 cubic feet at 315 feet. These wells together were responsible for the interest aroused and still exhibited over oil and gas possibilities in the vicinity of Oakland. Three other wells, all dry, were drilled, two in sec. 32 of East Oakland Township, and a third in southeastern Douglas County. The area lies a short distance east of the crest of the La Salle anticline, and therefore bears about the same relation to that structure as do the oil fields of Clark, Crawford, and Lawrence counties, for all along the anticline the dip is known to be consistently gentle toward the east. It is, however, not this major structure, but rather interruptions in the general inclination resulting in minor structures on the large fold, which have controlled oil accumulation in the southeastern fields. Ter- races and small or local anticlinal structures of the same sort doubtless exist in the Oakland area as well, but whereas drilling has been sufficient to determine the small but all-important structure in the oil fields, drill records about Oakland are so few and outcrops so rare that minor structures are still almost unknown. The problem is further compli- cated by the fact that such logs as are available indicate considerable irregularity in stratigraphy across the anticline north of Clark County. Indeed, so different are the conditions in Clark County at Westfield from those south of Oakland, that correctness of the correlation of a shallow sand at Westfield with one at Oakland is very doubtful. There are in- dications that the depth of the heavy Mississippian limestone (the "Big Lime") is much less in Clark County than it is near Oakland, and that there may be sands present near Oakland not found in Clark. The area should be drilled without regard to conditions in Clark County, and the records of the successive wells carefully kept in order to determine the actual sequence of strata. A thorough drilling of one of the persistent coal beds that underlies this region and is apparently of workable thick- ness, might probably be a venture worth the effort in itself, while at the same time it would reveal the structure in detail and indicate where deeper drillings for oil should most properly be located. Without some such preliminary investigation, prospecting in Coles and Douglas conn- ties must remain essentially a "wildcat" proposition. 14 OIL INVESTIGATIONS Crawford County The number of wells drilled fell from 276 in 1917 to 201 in 1918 and the number of producers from 205 to 139, the average new pro- duction per well being 8.9 and 8.1 barrels respectively. A 165-barrel well in Robinson Township on the Ferriman farm in 1917 and two 100- barrel wells on the Curtis and Turner farm in Licking Township in 1918 were the big producers of the two years. A number of 50 and 75-barrel wells were drilled during the same period but the majority gave yields considerably smaller. The activity evinced in Honey Creek Township in 1916 continued on into 1917 and 1918, although in some months Licking and Robinson townships surpassed Honey Creek in number of completions. Lawrence County As in the other counties of the southeastern Illinois field, new wells were comparatively few, 133 wells in 1917 and but 71 in 1918, although 246 wells was the total for 1916. The greatest activity was in Dennison Township from which two 200-barrel wells and a number of others al- most as large were reported during 1917 and 1918. The Kirkwood and Tracy sands, at a depth of 1,800 feet more or less, gave these large yields. Wabash County The best of a number of good producers brought in during 1917 and 1918 in the Allendale pool were three 100-barrel wells on the Courter lease. The total number of completions fell from 28 in 1917 to 18 in 1918 and the number of producers from 12 to 5, respectively. The average initial production per well for the county was 37.1 barrels in 1917 and 12.3 barrels in 1918. Excitement over the possibility of the discovery of a pool in Friends- ville Township began with the successful completion in October, 1917, of the Midland Oil and Gas Company's well on the Toney farm with an initial production of 40 barrels. The second well on the Toney farm was completed, dry, at 1,650 feet in January and by the following May a third well on the Toney farm and five others on the Price, McNair, Couch, Anderson, and Matheny farms had been reported as dry. A test on the Putnam farm in September of 1918 resulted in another dry well to be added to the list. Further testing will probably be very slow in view of the fact that so large a number of holes were dry in the near vicinity of the producer. PETROLEUM IN ILLINOIS IN 1917 AND 1918 15 SOUTH-CENTRAL ILLINOIS Macoupin County Only three wells were drilled during the past two years in Macou- pin County, two of them in 1917 and the other in 1918. The 1918 hole and one of the 1917 wells were drilled on the flank of the Staunton dome but were unsuccessful. The Loveland test drilled in Brushy Mound Township, well up on the southern swell of the Spanish Needle Creek dome, 1 was completed, dry, at 537 feet in February, 1917, and seems to indicate that oil will probably not be found at such depths in the structure, though the possibility of oil from deeper sands is not con- demned. The Staunton gas was substituted for artificial gas at Belleville, Edwardsville, Collinsville, Marysville, and Staunton late in 1916, and its use continued through 1917 and well into 1918, but the field began to show signs of early and rapid exhaustion in the latter part of 1918, necessitating return to artificial gas in some of these towns. Whether or not production can be revived sufficiently to take care of all or even a part of the area once supplied from this field is a doubt- ful question, the answer depending on whether the rapid decrease in pressure and flow experienced recently is due to actual exhaustion of the gas or to the ill effects of water caused by indifferent well procedure. Clinton County In 1917, of the 10 holes drilled, only one, that of the Ohio Oil Com- pany on the Niemeyer farm, was successful, 10 barrels being reported as the initial production at 941 feet. The dry holes were distributed as follows : three in Irishtown Township and one each in Clement, Breese, Meridian, Lake, and Carrigan townships. In 1918, of the 9 holes drilled, four were producers. Three of these were inside wells, two of them having an initial yield of 15 barrels, and one of 3 barrels. The Shaffer well in Irishtown Township, an outside location, gave 2 barrels as its initial yield. The Rogan test also in Irishtown Township resulted in a small production of gas at 1,149 feet. Marion County Marion County's record for 1917 and 1918 is extremely poor, with one gas well and no oil as the outcome of eight tests in the two years. 1 Lee, Wallace, Oil and Gas in the Gillespie and Mt. Olive quadrangles, Illinois: 111. State Geol. Survey Bull. 31, p. 102, 1915. 16 OIL INVESTIGATIONS Six tests were in the Centralia-Sandoval area, and two to the northeast in wildcat territory at Alma and at Kinmundy. The latter well was abandoned at 1,918 feet with no showing of oil or sand, although the depth seems sufficient to have reached the Stein and Benoist sands which produce oil at Sandoval. WESTERN ILLINOIS The statement made for 1916 may be pertinently repeated for 1917 and 1918, so far as new developments are concerned. The results of wildcat drilling in western Illinois served to emphasize further the "spotty" character of the Hoing oil sand. It is certain that favorable geological structure exists outside the Colmar-Plymouth fields but the prevailing absence of the sand is a discouraging feature. One 10-barrel well on the MacAllister lease and a number of 5- barrel and smaller wells were completed in the Plymouth-Colmar area. Out of a total of 22 wells drilled there, but 5 were dry and the average initial production was approximately 3 barrels per well in 1917. Activ- ity in 1918 was notably decreased. No wells were reported for Han- cock County, and but eleven for McDonough. None was dry, however, and an average initial production of 5.7 barrels is credited to this group. One dry hole in Schuyler County was the only outside test of which the Survey has record in western Illinois during the two years. It was drilled to a depth of 465 feet and abandoned. The Pike County field received attention during 1917. This shallow- gas field, discovered in 1886 but not developed to any extent until 1905, has just been investigated by the Survey largely in response to demand of the residents of the area. The interest was roused by the decrease in pressure which has become gradually more apparent in the past few years, as well as by the possibility of finding oil in commercial quanti- ties, and a report on the area is included as a part of this bulletin. Of the four 1917 wells, three were drilled for oil. The Ohio Oil Company made two tests in New Salem Township, one dry at 616 feet and the other giving a show of oil at 619. Claud Shinn drilled a 634- foot well in Perry Township that showed oil at 650 feet. SOUTHERN ILLINOIS Dry holes were drilled in southern Illinois as follows during 1917 and 1918: NE. Y\ SW. Y\ sec. 35, Elvira Township, Johnson County, depth 2,000 feet; sec. 12, Raleigh Township, Saline County; sec 28, Eldorado Township, Saline County, depth 1,950 feet; and sec. 32, Omaha Township, Gallatin County. Drilling on the Campbell Hill anticline nc:w PETROLEUM IN ILLINOIS IN 1917 AND 1918 17 Ava in Jackson County 1 resulted in the discovery of additional gas wells but as yet there has been no commercial utilization of the product. NORTHERN ILLINOIS No tests have been made as yet in response to the discovery of a seep of oil and gas along a small fault plane near Coal City, described in a previous bulletin. 2 In McLean County two dry holes were put down, one at Downs and the other at Le Roy. Whether or not these holes should be con- sidered as condemning the structure locally is doubtful, owing to the fact that the location of the axis of the La Salle anticline in this area is not known definitely. That it passes northwest in the general vicinity of McLean County, seems clear, but drilling has been so meager and scattered that determination of the axis exactly has been impossible. MISCELLANEOUS DRILLING One test credited with an initial production of two barrels and not mentioned above was drilled in Madison County in 1917 on the Keller farm, in sec. 8 of Collinsville Township. Other holes not already noted, all of them dry, were drilled as follows during 1917 and 1918 : 1917 County Township Section Bond La Grange 21 La Grange 28 Burgess 34 Edwards Shelby 35 Fayette Lone Grove 12 Madison Saline 27 Omphghent 13 Collinsville 8 Helvetia 12 Hamel 10 Hamel 15 Morgan Waverly 22 Perry T. 5S..R.1W 4 Randolph Sparta (?) Washington Irvington, 2 holes 26 *St. Clair, Stuart, The Ava area: 111. State Geol. Survey Bull. 35, pp. 57-65, 1917. 2 Kay, F. H., Petroleum in Illinois in 1916: 111. State Geol. Survey Bull. 35, pp. 16-17, 1917. 18 OIL INVESTIGATIONS 1918 County Township Cumberland , . . . Crooked Creek Douglas Sargent Madison Olive Olive. Washington Irvington County 36 35 9 15 26 SUMMARY TABLES The following tables summarize oil development in Illinois during 1917 and 1918. Tables 3 and 4 are compiled directly from the Oil City Derrick. Tables 5 and 6 are compiled from the same source with addi- tions by the author, which accounts for the difference in total. It was impossible to include additions in Tables 3 and 4 because in most cases the month of completion was not known, while for Tables 5 and 6 this information was not necessary. The total number of wells drilled to January 1, 1918, was 25,997 of which 4,825, or 18.6 per cent, were dry. Similar statistics for Janu- ary 1, 1919, are 26,407 wells, 4,945 of which, or 18.9 per cent, were dry. Table 3. — Monthly record of wells drilled in Illinois, 1917 Month Completed New production Dry holes Averag-e initial production Abandoned wells Gas wells January February March April May 66 46 40 55 64 61 73 72 47 48 41 36 1,165 790 384 694 1,020 1,161 861 1,437 1,091 672 509 354 14 17 13 13 13 10 23 15 9 8 10 11 22.3 27.3 14.2 16.9 20.8 23.0 16.0 24.5 30.3 17.2 16.4 15.9 11 12 14 15 9 12 20 15 26 22 33 13 1 2 2 June July 1 August September. . . . October November December 2 1 Total 1916 649 1,459 10,138 24,713 156 317 20.9 22.3 202 145 9 36 PETROLEUM IN ILLINOIS IN 1917 AND 1918 Table 4. — Monthly record of wells drilled in Illinois, 1918 19 Month Completed New production Dry holes Average initial production Abandoned wells Gas wells January. . February. March April May June July August . . . September October. . . November December. Total... 1917 13 248 4 27.6 21 1 5 11 1 3.7 2 1 27 308 9 17.2 1 38 378 12 14.5 22 1 30 454 8 23.7 10 3 41 470 9 14.7 20 46 978 13 30.6 31 1 49 676 17 19.2 30 38 950 11 35.2 26 1 25 369 5 19.5 18 , . 42 498 13 11.8 7 1 42 559 11 13.3 26 396 5,899 113 19.3 214 9 649 10,138 156 20.9 202 9 Table 5. — County record of wells drilled in Illinois, 1911 County Completed New production Dry holes Abandoned wells Gas wells Bond a Clark: Clinton Coles Crawford Cumberland Edgar Edwards* Fayette a Hancock Jackson 8 Jasper Johnson" Lawrence McDonough McLean 8 Macoupin 8 Madison 8 Marion Montgomery 8 . . . 3 137 9 1 276 26 6 1 1 4 2 1 133 18 2 2 7 6 1 1,439 10 3,103 148 40 15 4,297 46 3 21 8 1 71 1 5 1 1 1 2 1 19 4 2 2 6 5 1 22 6 63 93 1 11 20 OIL INVESTIGATIONS Table 5. — County record of wells drilled in Illinois, 1911 — Concluded County Completed New production Dry holes Abandonee wells [ Gas wells Morgan a 1 2 4 1 2 28 1 5 Perry Pike a 1,040 2 2 1 2 16 Randolph 3 Saline Wabash Total 674 10,140 179 202 9 Added by author. Table 6.— Comity record of wells drilled in Illinois, 1918 County Completed New production Dry holes Abandoned wells Gas wells 71 560 11 15 9 35 5 3 1 5 4 1 201 2,482 62 96 6 1 1 1 1 2 6 10 4- 6 3 5 1 71 2,601 13 98 11 63 1 1 2 2 2 2 18 146 13 2 2 2 •• 410 5,899 121 214 14 Clark Clinton Coles Crawford . . . Cumberland , Douglas a Edgar Jackson a . . . . Jasper Lawrence . . . McDonough. Macoupin a . . Madison a . . . Marion Wabash .... Washington . Total Added by author. BROWN COUNTY By Merle L. Nebel OUTLINE PAGE Introduction 22 Acknowledgments 22 Method of field work 23 Personnel of party 23 Key horizons 23 Physiography 24 Stratigraphy 25 General statement 25 Unconsolidated rocks 25 Alluvium , 25 Loess 25 Glacial drift 26 Consolidated rocks 27 General description 27 Rocks outcropping in the region 28 Carbondale formation 28 Pottsville formation 30 St. Louis limestone 31 Salem limestone 32 Warsaw formation 36 Keokuk formation 37 Rocks known only from drill records 38 Burlington limestone 38 Kinderhook and Upper Devonian shales 38 Devonian limestone 38 Niagaran dolomite 39 Ordovician rocks 39 Possible oil-producing horizons 40 Structure 41 General statement 41 Relation of structure to accumulation of oil 43 Detailed structure 44 Localities previously tested 46 Recommendations 49 (21) 22 OIL INVESTIGATIONS ILLUSTRATIONS PLATE PAGE I. Map of Brown Gounty,. showing structural contours based on the elevation of No. 2 coal above sea level 46 FIGURE 2. Entrenched meanders. .'. 25 3. Large mass of Pennsylvanian shale and coal imbedded in glacial drift 27 4. Nodular limestone 30 5. Bluff of Carbondale and Pottsville 31 6. Cross-bedding in Salem limestone 32 7. Peculiar weathering of argillaceous Salem limestone 33 8. Massive brown dolomite ( Salem ) 34 9. Contact of Salem dolomite and Warsaw shale 35 10. Brown dolomite grading laterally into shale 35 11. Local unconformity between Salem and Warsaw 36 12. Unconformity between Salem and Warsaw 37 13. Diagram, to scale, of unconformity, the left half of which is photographed in figure 12 38 14. Diagrams showing conditions governing oil accumulation 42 INTRODUCTION The purpose of this report is to present the results of a survey of Brown County made during the fall of 1917. It attempts to describe briefly the general geology of the region, but the principal object is to point out the rock structure and its relation to possible accumulations of oil or gas. Figure 1 shows the area covered by the report. Acknowledgments Professors T. E. Savage and Stuart Weller of the Geological Sur- vey staff were freely consulted in connection with the correlation of the Salem and St. Louis formations, and their assistance is gratefully ac- knowledged. Professor Savage in addition gave valuable assistance in reading the manuscript. The work was begun under the direction of J. L. Rich, who made a preliminary study of the region and selected certain key horizons which could be readily identified and used as a basis for determining the structure. His work covered approximately the northern half of the county, except for a small area worked out by Morse and Rich in 1914. 1 The southern half of the county was worked by the author. 1 Morse, W. C, and Kay, F. H., Area south of the Colmar oil field: Illinois Stale Geol. Survey Bull. 31, p. 10, 1915. BROWN COUNTY 23 Method of field work It is known that practically all folding in the area under consid- eration took place after the deposition of the youngest of the consoli- dated rocks, and therefore structural deformations of the oil sands are reflected in the hard rocks appearing at the surface. The method of work was based, then, upon the fact that the rock layers at some depth, in- cluding all oil-bearing horizons, lie essentially parallel to those outcropping at the surface. Definite beds that could be easily recognized by the geologist were selected as key horizons, and the structure determined by running instrumental levels to each bed. The field party was composed of a geologist in charge, a transitman, and two rodmen. The geologist identified the key horizons, such as coal beds or limestones, and measured the intervals between them. He se- lected numerous points, spaced as uniformly as possible, where the key rocks were exposed and at which elevations were later obtained by the transit party under his direction. An early method of marking these points so that they could be recognized by the transit party was to place upon them flags consisting of cheesecloth squares on a lath staff. Each point was located on the map by the pacing and compass method, and a copy of the map furnished to the transitman. So much difficulty was encountered in finding these flags in wooded areas that another method was devised. Instead of placing a flag the geologist carried a hand- level line to some prominent object a few paces away, such as a large blazed tree, a gate post, etc., and carefully described it in his notes. This object was numbered with crayon or paint and the transit party fur- nished with a copy of the description as well as a copy of the map showing locations of all points. With this method the geologist was enabled to keep his work several weeks in advance of the leveling. Personnel of Party The party, in addition to Messrs. Rich and Nebel, included at dif- ferent times R. Pinheiro, D. D. Sparks, A. H. Thurston, Paul Birming- ham, George Burgesser, and William Calvo. Key Horizons The principal key horizon used in determining the structure is a thin coal bed known as No. 2 (Colchester) of the Illinois section. It outcrops at numerous points throughout western Illinois, is uniform in thickness, and is easily identified. In areas where this coal does not out- crop other rocks either below or above it were used as key horizons, and the intervals between these rocks and the coal were measured as fre- 24 OIL INVESTIGATIONS quently as possible. The horizons used and the distance between each one and No. 2 coal are as follows : 8. Base of third nodular limestone 125 feet above top of No. 2 coal. 7. Base of Chonetes limestone, 112 feet above top of No. 2 coal. 6. Base of second nodular limestone 98 to 102 feet above top of No. 2 coal. 5. Base of shaly, fossiliferous limestone, 20 to 41 feet above top of No. 2 coal. 4. Top of No. 2 coal. 3. Base of first nodular limestone, 9 to 17 feet below top of No. 2 coal. 2. Top of Salem limestone 24 to 50 feet below top of No. 2 coal. 1. Base of Salem limestone 50 to 70 feet below top of No. 2 coal. As soon as the elevation of any key horizon was determined, the hypothetical elevation of No. 2 coal at that place was computed by adding or subtracting the interval between the two as measured in the nearest exposure. The top of the Salem limestone is second in importance to the top of No. 2 coal as a key horizon, and was used frequently in the south- eastern portion of Brown County. The interval between the two is var- iable, but by measuring it frequently and using the nearest measurement to a given exposure in computing the hypothetical elevation of the coal, results were obtained which are believed to be reliable. PHYSIOGRAPHY Brown County lies on the eastern slope of the divide between the Mississippi and Illinois rivers. The surface of the central and west central portions of the county is a flat, undissected prairie sloping gently to the east. The northern portion is drained by Crooked Creek and its tributaries, the eastern quarter by small creeks flowing directly into Illi- nois River, and the southern third by McGees Creek, which flows from east to west across the county and empties into the Illinois a few miles below Perry Springs. Timewell is 756 feet above mean sea level, and at the Mount Sterling water tower the altitude falls to 735. At Hers- man it is 695, at Gilbirds it is 662, and at Versailles, 588. The flood plain of Illinois River lies at an elevation of about 440 feet above mean sea level, that of Crooked Creek at about 440 to 450, and that of Mc- Gees Creek at 450 south of Versailles to 550 south of Siloam. There is a maximum relief of 300 feet, and the county as a whole is hilly and rough except in the central and western portions. The valley sides are usually steep and the flood plains narrow. An interesting example of en- trenched meanders (fig. 2) was noted in the SE. % sec. 18, T. 2 S., R. 3 W., near the head of a small intermittent stream which flows southeast into McGees Creek. BROWN COUNTY 25 STRATIGRAPHY General Statement The hard rocks of the region are almost everywhere covered by a mantle of unconsolidated clay, sand, and gravel. These unconsolidated rocks consist of material deposited in the valleys by the present streams, and called alluvium, of fine material deposited by the wind, and called loess, and of material deposited by the continental glaciers, known as drift. The hard rocks are ordinary shales, sandstones, and limestones. Unconsolidated Rocks alluvium The alluvium deposited by the streams consists of fine sand, gravel, and clay which has been washed away from the hills and carried into Fig. 2. Entrenched meanders. The curved cliff in the center of the photograph is of Salem limestone and is about 20 feet high. the valleys of such streams as McGees and Crooked creeks and Illinois River. Its greatest thickness is reached in the valleys of Crooked Creek and Illinois River. A deep well drilled near Crooked Creek passed through 210 feet of alluvium before reaching bed rock. LOESS The loess is a fine, yellow, wind-blown dust which covers the up- lands to a depth of several feet. It is usually thicker along the bluffs overlooking the valleys and thinner back on the uplands. Along the bluffs of Illinois River it is in places as much as 100 feet thick, but over 26 OIL INVESTIGATIONS most of the county is only a few feet thick. Because of this peculiar distribution, it is generally believed that the fine-grained material which forms the loess has been picked up from the flood plains of the larger val- leys and spread over the adjacent territory by the wind. A prominent char- acteristic of loess is its tendency to stand in vertical cliffs where ex- posed by stream erosion, GLACIAL DRIFT The glacial drift underlies the loess, and overlies and conceals the bed rock throughout the region except where it has been cut through by the streams. It consists of a blue or yellow boulder clay (Illinoian till) with occasional layers or beds of sand or gravel. The clay contains num- erous boulders or pebbles of many different kinds of rock, usually of the harder varieties, such as granite, diabase, quartzite, limestone, etc., which have been carried great distances by the glacier and deposited with an unsorted mass of sand and clay. Soft rocks, such as shale, have been ground up for the most part into a fine clay, but occasionally a mass of shale like that underlying the glacial drift over much of the county was picked up and moved a short distance by the ice without being greatly broken up. Such a mass is shown in the accompanying photograph (fig. 3). It is about 30 feet long by 15 feet thick and consists of ordi- nary gray and blue shale with nearly a foot of coal at the base. It is tilted at an angle of about 30° but remains unbroken, although it is com- pletely imbedded in yellow till which is well exposed above and below and on either side. This mass of shale and coal lies below the level of the top of the Salem limestone, which is stratigraphically 25 feet or more below the level of any coal-bearing strata at this locality. The thickness of the drift averages about 30 to 40 feet over the county as a whole. The greatest thickness is over preglacial lowlands and the maximum noted is 120 feet. Consolidated Rocks general description The known consolidated rocks underlying this area include all those formations from the lower part of the "Coal Measures" down to the St. Peter sandstone. Only Pennsylvanian and Mississippian rocks outcrop in the county, and include the Carbondale and Pottsville formations of the Pennsylvanian system, and the St. Louis, Salem, Warsaw, and Keo- kuk formations of the Mississippian system. The rocks lying below the Keokuk are known only from the records of wells which have been drilled through them. Nothing is known of the rocks below the St. Peter sandstone, for no wells have been drilled through it in this region. BROWN COUNTY 27 Pennsylvanian rocks belonging to the Carbondale and Pottsville formations underlie the drift over about three-fourths of the county, but in places in the southeastern portion they were completely eroded before glacial times, and glacial drift lies directly upon Mississippian limestones. The accompanying generalized section will give an idea of the character and thickness of the different formations exposed at the sur- " "* «H„ • *' %»*v ^^ r 4 ••. '*":'>' : M> : ',-*■ p\s39i wSM '*•*• ■ v % .-.. . »?.':< '«vw ,; ;: ^ ...J - "rMz ''■ '~<:'\\-- :: '"'"■ ^-fSi^XVv;: '^ ' ' ' ' : ' ' ' -'",-. , ■ ■- : ;.''>' :; ' '. . ' - ^P«B| ?\ j4 ' ■■■■■■■: 1 ^tj ' J§f}.: : - -ft ■'V*.--'" : ^.^pPP«( BKiflp^ ' : ' '■■<■ "■'' t; >' i ' ' * .: ■ -^ . ..: '■;.."•.■ : ;■ f ,::fv-.;> ■ ■ ■ ;•■;.;:■■■"■ ■■■- :.' > v . ^ ,;" ; ::: ; Pig. 3. Large mass of Pennsylvanian shale and coal imbedded in glacial drift in SW. % SW. % sec. 26, T. 1 S., R. 2. W. face or explored in deep drilling in this area, and their relations to one another. Generalized section of hard rocks in Brown County Pennsylvanian system — ■ Carbondale formation; consists of shales, sandstones, thin limestones, and No. 5 and No. 2 coals. Upper limit is the top of No. 6 (Herrin) coal which is not present in this area, and lower limit is the base of No. 2 coal. Maximum thickness in Brown County is about 130 feet. Pottsville formation; soft gray or white clay shale (fire clay), sandstone, and a thin limestone; from the base of No. 2 coal to the top of Mis- sissippian limestone. Thickness variable; 6 to 50 feet. Mississippian system — St. Louis limestone; white limestone conglomerate or breccia near top, fine-grained buff or gray dolomite below; much broken and with green shale partings. Thickness 8 to 26 feet. Salem limestone; green to brown sandstone above and gray or brown granular, fossiliferous limestone below. Both sandstone and limestone were formerly quarried extensively for building stone. Thickness 18 to 35 feet. 28 OIL INVESTIGATIONS Generalized section of liarcl rocks in Brown County — Concluded Warsaw formation; gray .shales with thin, lenticular limestone beds. Geodes are abundant in the shales, and both limestones and shales are crowded with bryozoan remains. Thickness 30 to 55 feet. Some- times as much as 80 feet is reported in drill records but this probably includes much of the Salem and Keokuk. Keokuk limestone; thin-bedded, cherty limestone with abundant fossils. It outcrops in only one locality in Brown County where an exposure 24 feet thick was noted. Normal thickness 40 to 75 feet. Burlington limestone; white, fossiliferous limestone (crinoidal) with abundant chert. Not exposed in Brown County. The St. Louis, Salem, Warsaw, Keokuk, and Burlington formations where penetrated in drill holes are grouped together and called the "first lime" or "Mississippian limestone". The total thickness of this group as shown in well records is from 325 to 350 feet. Kinderhook shale; gray shales, not exposed in Brown County and known only from drill records. Thickness 80 to 100 feet. In drill records it is usually not distinguished from the underlying Upper Devonian shale. The two have a thickness of 160 to 200 feet. Devonian system — Upper Devonian shale; brown shales with numerous spores of Sporangites. Thickness 20 to 100 feet. Not exposed in Brown County and in well records is commonly grouped with Kinderhook shales, the two together having a thickness of 160 to 200 feet. Devonian limestone; known only in drill records and usually grouped with the Niagaran, the two having a thickness of 10 to 75 feet. In rare cases neither limestone is found. Silurian system — Niagaran dolomite; porous limestone or dolomite known only in drill records and grouped with the Hamilton. Thickness 10 to 75 feet. It is in this limestone that the gas of the Pike County gas field occurs. Sometimes a porous sandstone occurs at the base of the Niagaran. This is the rock which produces the oil of the C'olmar oil field and is known as the "Hoing sand." When present it varies in thickness from a few inches to 30 feet or more. Ordovician system — Maquoketa shale; gray and brown shales, usually 180 to 200 feet thick. Kimmswick-Plattin limestone; gray limestone penetrated only by very deep wells. Usually 200 to 400 feet thick. St. Peter sandstone ; a pure white, clean sandstone, containing large quanti- ties of water. This is the rock which furnishes the water in the deep well at Mount Sterling at a depth of 2,433 feet. Only the deepest wells penetrate it. ROCKS OUTCROPPING IN THE REGION CARBON DALE FORMATION The Carbondale formation consists of gray shales with thin beds of limestone, sandstone and coal. It includes No. 2, No. 5, and No. 6 coals, but in Brown County No. 6 is absent, and No. 5 is rarely found. No. 2 BROWN COUNTY 29 coal is distributed widely over the county from north to south, and its uniform thickness, easy identification, and wide distribution make it by far the best key horizon for determining the structure. A composite section of this formation, showing its normal char- acter in the north half of the county is as follows : Generalized section of the Carbondale formation in the north half of Brown County Thickness Feet inches 14. Shale, gray 5 13. Limestone, white, nodular (key horizon No. 8) 2 6 12. Shale, gray 11 11. Limestone, gray, with Chonetes t and Spirifer cameratus (key horizon No.- 7) 1 10. Shale, gray 13 9. Limestone, white or light gray, heavy nodular (key hori- zon No. 6 ) 5 8. Clay shale, soft, gray or blue 6 7. Sandstone and sandy shale 10 6. Shales, blue gray, sandy 59 5. Limestone, shaly, fossiliferous (key horizon No. 5) 2 6 4. Clay shales, blue, sandy 20 6 3. Limestone, black, septarian 1 Z. Shales, black, bituminous, thin-bedded (black slate) .... 3 1. No. 2 coal (key horizon No. 4) 2 141 6 The upper part of this section is found only in the northern half of the county. The heavy nodular limestone (key horizon No. 6) is found as far south as the headwaters of Dry Fork in sec. 18, T. 1 S., R. 3 W., and sec. 13, T. 1 S., R. 4 W. (See figure 4.) The maximum thickness of the Carbondale found south of these points is 60 feet. On the whole, the strata of the Carbondale are very uniform in thickness, although there are local variations. No. 5 coal is absent except in one or two localities. It has been mined in sees. 8 and 9, T. 1 S., R. 3 W., in the valley three-quarters of a mile north of Mount Sterling, where it is iy 2 to 3 feet thick and lies 15 to 17 feet above the heavy nodular limestone (key horizon No. 6). The black carbonaceous shale above No. 2 coal varies locally in thickness and in its position above the coal. In the southern half of the county it almost invariably lies directly on the coal, while farther north 3 to 8 feet of blue shale may intervene between the two. This black shale bed, together with the zone of large septarian con- cretions of black limestone above it, makes the. identification of No. 2 coal easy. 30 OIL INVESTIGATIONS POTTSVILLE FORMATION The Pottsville formation includes all strata from the base of No. 2 coal to the top of the Mississippian limestone. It is made up principally of shale or sandstone with an occasional bed of thin coal or limestone. Its thickness is extremely variable. North and east of Mount Sterling it is in places as much as 50 feet. On the hill at La Grange, near the center of sec. 29, T. 1 S., R. 1 W., the following section was measured : Section measured near center of sec. 29, T. 1 8., R. 1 W. Thickness Feet 14. Drift and loess 105 13. Shale, sandy 15 12. Shale, black, carbonaceous 3 11. No. 2 coal (key horizon No. 4) 1 10. Shale and underclay . 7 9. Limestone, white, nodular (key horizon No. 3) 5 8. Shale, gray 3 7. Shale, sandy 3 6. Clay shale, weathers out white 9 5. Coal 4. Sandstone, ferruginous 5 3. Shales, sandy, and clay 9 2. Limestone, ( St. Louis) 12 1. Dolomite, sandy (Salem) (key horizon No. 2) 20 inches 199 Fig. 4. Nodular limestone near center of sec. 8, T. 1 S., R. 3 W. BROWN COUNTY 31 The Pottsville here includes members 3 to 10 with a total thickness of 41 feet 4 inches. South of Mount Sterling and over the southern half of the county the Pottsville is rarely over 15 feet thick, and it consists almost entirely of a soft, white or light-gray clay shale with an occasional lens of sand- stone. The shale frequently contains many crystals of gypsum. Along McGees Creek and its tributaries the thickness varies from 7 to 15 feet. (See Fig. 5.) The Pottsville usually lies upon the St. Louis limestone, but in a few instance exposures were found where the St. Louis has been completely eroded and the Pottsville rested directly upon the Salem limestone. Fig. 5. Bluff of Carbondale and Pottsville in NW. % sec. 17, T. 2 S., R. 4 W. Pottsville from base of No. 2 coal (behind man) to St. Louis limestone in creek bed is 7% feet thick. ST. LOUIS LIMESTONE The St. Louis limestone is the youngest formation of the Missis- sippian system found in this region. It formed an old land surface previous to the deposition of the Pottsville rocks and consequently has been partially, sometimes completely, removed by erosion. The maxi- mum thickness found in this region is 26 feet. The upper part consists of a very characteristic white limestone conglomerate or breccia, and the lower part of poorly bedded, very fine-grained, gray or buff dolomite. It is generally unfossiliferous except for the upper few feet in which the corals Lithostrotion proliferum and Lithostrotion canadcnse are in 32 OIL INVESTIGATIONS places abundant. A prominent feature of the St. Louis is the presence of thin stringers and layers of bright-green shale, which varies from a mere parting to two feet thick. The following section is typical of the more complete exposure of St. Louis in this region : Measured section of St. Louis formation near center of sec. 16, T. 2 S., R. 4 W. Thickness Feet 6. Limestone, light gray, with abundant branching corals (Lithostrotion proliferum) 3 5. Limestone, white, brecciated 10 4. Shale, green 3. Dolomite, broken, light gray 1 2. Dolomite, fine grained, sandy 7 1. Shale, green , 1 inches 23 Fig. 6. Cross-bedding in Salem limestone, SE. % Sec. 8, T. 2 S., R. 3 W. SALEM LIMESTONE Underlying the St. Louis limestone, and unconformable with it, is the Salem limestone. This formation is extremely variable in character and may consist of gray, crystalline limestone, of limestone and sand- stone, or of a very sandy brown dolomite. In many cases it is extremely difficult to determine an exact line of contact between it and the over- BROWN COUNTY 33 lying St. Louis, or the underlying Warsaw. Where the gray crystalline limestone occurs it contains numerous fossils and can easily be identified. Following is a list of specimens collected from this horizon in the NE. 34 sec. 24, T. 2 S., R. 4 W. : Fenestella sp. Productus altonensis Echinoconchus biseriatus Camarotoechia mutata Eumetria verneuiliana Spirifer bifurcatus Spirifer sp. Composita trinuclea Aviculopecten talboti Leperditia carbonaria Professor T. E. Savage has examined the fossils and confirmed the identification of the limestone as Salem in age. Fig. 7. Peculiar weathering of argillace- ous Salem limestone, SW. % sec. 23, T. 2 S., R 4 W. In this phase it closely resembles the well-known Bedford limestone and has an oolitic appearance due to the presence of small rounded shells of the foraminifer, Endothyra baileyi. It is nearly always cross- bedded and this cross-bedding is sometimes so perfect that the rock splits into thin, parallel plates. (See figure 6.) The thickness varies from 12 to 30 feet. It is usually sandy near the top and frequently grades upward into a bright green, non-f ossiferous, calcareous sand- 34 OIL INVESTIGATIONS stone which is generally 2 to 5 feet thick, but which may attain a thick- ness of 12 to 15 feet. When this sandstone is absent the gray limestone lies directly below the St. Louis. Another phase of the- Salem is a soft, gray, argillaceous limestone which in places lies directly below the St. Louis and is from 10 to 15 feet thick. This rock is poorly bedded and weathers in a peculiar man- Fig. 8. Massive brown dolomite (Salem), SW. % sec. 26, T. 2 S., R. 3 W. ner. On vertical outcrops it scales off at right angles to the bedding in thin, irregular, curved plates from a few inches to two or three feet across and an inch or less in thickness. (See figure 7.) This is prob- ably a result of frost action. The lower part of the Salem is usually a massive, brown, sandy dolomite (fig. 8) which may lie in sharp contact with the underlying Warsaw shales (fig. 9) or which may grade so gradually into shale both laterally and vertically that it is impossible to draw a sharp line be- tween the two formations. (See figure 10.) Although most exposures BROWN COUNTY 35 Fig. 9. Contact of Salem dolomite (above) and Warsaw shale (below), SW. % sec. 17, T. .2 S., R. 3 W. Fig. 10. Brown dolomite grading laterally into shale, NW. ^4 sec. 4, T. 3 S., R. 3 W indicate continuous deposition from Warsaw to Salem, in one or two cases local unconformities occur between the two. (See figures 11, 12, and 13.) 36 OIL INVESTIGATIONS WARSAW FORMATION The Warsaw formation, as exposed in this region, consists prin- cipally of blue, calcareous' or clay shales with thin, lenticular limestones. Both shales and limestones are fossiliferous, bryozoans being especially abundant. The lenticular nature of the limestones is worthy of note, for although a number of such beds occur, they are of small areal extent, and it was found impossible to trace a single bed from place to place so that it might be used in working out structure. Geodes are common in both the shales and the limestones of the Warsaw formation. The max- imum thickness noted was 55 feet, but in some of the deep wells 80 feet of shale has been reported. This probably includes a part of the Keokuk formation. Fig. 11. Local unconformity between Salem and Warsaw. Salem limestone (above) dipping to the right; Warsaw (below) horizontal. The following section is typical of the Warsaw of ihis region: Measured section of the Warsaiv formation along a stream in SE. 14 sec. 18, T. 2 8., R. 3 W. Thickness Feet inches 15. Shale, blue, calcareous 2 6 14. Clay shale, soft, blue, unfossiliferous 6 13. Limestone, geodiferous, with abundant fossils 1 6 12. Clay shale, blue, full of geodes 2 11. Clay shale, blue 2 10. Limestone, with abundant fossils 2 6 BROWN COUNTY 37 Measured section of the Warsaw formation — Concluded Thickness Feet inches 9. Shales, sandy, with thin lenses of limestone, fossiliferous 4 8. Clay shales, soft, blue 6 7. Limestone, sandy, full of fossils . . 8 6. Clay shales, soft, blue, with abundant bryozoans 2 5. Clay shales, soft, blue, free from fossils 12 4. Geode bed 6 3. Clay shales, soft, blue 4 6 2. Clay shales, blue, alternating with thin, sandy limestone beds 4 1. Clay shales, soft, blue, exposed 7 57 2 Fig. 12. Unconformity between Salem (above), dipping to the right, and War- saw (below) horizontal, SE. 14 sec. 19, T. 2 S., R. 3 W. KEOKUK FORMATION The Keokuk formation of this region consists of an upper bed of shale which is crowded with geodes for the most part, and a lower mem- ber of gray, crystalline limestone with numerous lenses and thin layers of chert. The Warsaw shales lie above the geode beds in perfect con- formity with them, and no attempt was made to distinguish between the two in this work. The geode beds outcrop along McGees Creek in the southwestern corner of the county. The lower limestone member outcrops at only one or two localities near the county line south of Benville, where a maximum thickness of 24 feet was measured. Fossils collected from this limestone were identi- 38 OIL INVESTIGATIONS fied as of Keokuk age by Stuart Weller of the University of Chicago. This limestone is the oldest rock which outcrops in the county. Nothing is known of the rocks lower down in the geological column, except from information obtained in drilling deep wells. Rocks Known Only From Drill Records BURLINGTON LIMESTONE Immediately below the Keokuk limestone is a thick, white limestone containing numerous masses of chert or flint. It is never distinguished from the Keokuk in ordinary drilling operations, but the two are re- ported together and have a thickness of 200 to 220 feet. They make up the lower part of the "first lime" or "Mississippi lime". Frequently the whole series from the top of the St. Louis to the base of the Burlington is included as the "first lime" and its total thickness is about 325 to 350 feet. Horizontal & vertical scale In feet Fig. 13. Diagram to scale, of unconformity, the left half of which is photo- graphed in figure 11. KINDERHOOK AND UPPER DEVONIAN SHALES Below the Burlington limestone, and forming the base of the Missis- sippian system is a thick bed of blue shale, known as the Kinderhook formation. Below it is usually found a brown shale of Upper Devonian age, which contains numerous tiny spores of the plant known as Sporangites huronense. The two shale beds are rarely distinguished by drillers, but are reported together with a total thickness of 160 to 200 feet. DEVONIAN LIMESTONE A thin, gray, non-magnesian limestone is usually found immediately below the Upper Devonian shales. This is believed to be the late Mid- BROWN COUNTY 39 die Devonian limestone of the northwest Illinois and Iowa province. It is rarely more than 15 feet thick. It is difficult to distinguish it from the underlying Niagaran limestone, which, however, is usually a very porous pink dolomite. The two together are reported by drillers as the "second lime." NIAGARAN DOLOMITE Below the Devonian limestone is frequently found a very porous, pink or gray dolomite of Silurian age, known as the Niagaran limestone or dolomite. It was deposited upon an irregular, eroded surface and was itself subjected to erosion before the deposition of the overlying Devonian limestone. In places it was completely removed so that the Devonian lies directly upon the Maquoketa shale, but ordinarily a few feet of Niagaran is included in the lower part of the "second lime" as reported by drillers. The greatest thickness reported for the two lime- stones is 70 feet. The Niagaran limestone is closely associated with oil and gas pro- duction in western Illinois. It is the "gas rock" of the Pike County gas field where wells drilled into it more than 30 years ago are still pro- ducing gas sufficient for farm use. Some of the w T ells in this field re- ported showings of oil as well as gas, and in one or two wells small quantities of oil have been produced and used for lubricating purposes. The rock is probably capable of acting as a reservoir for oil in commer- cial quantities, as well as gas. The "broken sand" often reported at the base of the "second lime" by drillers is probably this porous dolomite. The oil-sand of the Colmar oil field, known as the Hoing sand, lies just below the Niagaran dolomite. ORDOVICIAN ROCKS Below the Niagaran limestone the drill penetrates a succession of blue, green, and brown shales, called the Maquoketa shale. This forma- tion is from 180 to 200 feet thick. It has not been known to produce oil, but in the Walker well drilled by the Indian Refining Company, near the center of sec. 9, T. 2 N., R. 2 W. (Schuyler County), a showing of oil was reported at a depth of 751 feet, about 74 feet below the top of the Maquoketa shale. Below the Maquoketa in this region is the Kimmswick-Plattin limestone, generally known as the "Trenton." It is a gray, non-mag- nesian limestone, and in this region is 200 to 400 feet thick. It is pene- trated only by the deepest wells. It is not known to be oil-producing in western Illinois, although a few wells have been drilled into it. In 40 OIL INVESTIGATIONS southeastern Illinois a few deep wells are producing a small amount of oil which is believed to come from the Trenton. In Ohio and Indiana large quantities of oil have been produced from dolomitic areas in the Trenton limestone, and increased production from this horizon may pos- sibly be obtained in Illinois. Below the Kimmswick-Plattin limestone is the St. Peter sandstone, a clean, white sandstone which usually contains large quantities of water but is not known to be oil producing. The water from the deep well at Mount Sterling comes from this formation at a reported depth of 2,433 feet. The well is said to have been drilled to a depth of 2,675 feet. POSSIBLE OIL-PRODUCING HORIZONS Showings of oil or gas have been reported from several different horizons in the rocks which underlie this area, but in western Illinois commercial quantities of oil have been produced from only one such horizon. The oil produced in the Colmar field comes from a porous sandstone lying immediately below the Niagaran dolomite. This is known as the "Hoing sand," and it is this horizon which gives the most promise of producing oil in Brown County. Unfortunately it does not occur as a continuous bed extending throughout the region, but is found only in isolated lenses. This makes prospecting unusually hazardous, since it is impossible to predict in advance of drilling whether or not the sand will be present. The known areas underlain by this sand vary in extent from 4 or 5 square miles or less up to 40 or 50 square miles. The lens which furnishes most of the production in the Colmar field has an areal extent of about 10 square miles, but most of the production comes from less than half of this area. In general it appears that the sand bodies have a lenticular or oval shape, with their greatest diameter in a northeast- southwest direction. Where two or more lenses are known to lie in close proximity they have a northeast-southwest arrangement. It is still uncertain, however, whether this generalization can safely be used in prospecting. The thickness of the sand bodies varies from a few inches to 30 feet. The exact age of the Hoing sand has never been determined, but it is certainly early Silurian, and there is some evidence to indicate that it is of early Edgewood age. The shape and distribution of the sand bodies point either to deposition of sand in isolated low areas prior to the deposition of the overlying dolomite, or to extensive erosion after de- position of the sand, so that only isolated patches survived. BROWN COUNTY 41 Another horizon in which slight amounts of oil have been found is the Niagaran limestone or dolomite. It is very porous and is probably capable of serving as a reservoir for the accumulation of oil, although so far as known, oil has never been found in it in commercial quantities. A well drilled on the Claude Shinn farm, sec. 36, T. 5 S., R. 5 W., pene- trated porous Niagaran filled with a heavy, black oil which is almost as viscous as pitch. The Ohio Oil Company reported a heavy black oil from the Niagaran in the Seaborn well in sec. 6, T. 4 S., R. 4 W., Pike County. Gas is frequently reported by drillers, and in the Pike County gas-field wells have been producing from the Niagaran for many years. Slight showings of oil are occasionally found in the Maquoketa shale, and if a porous sandstone were present to act as a reservoir in which oil could accumulate, it is not unlikely that this formation might be- come productive, but no such accumulations have been found. In the Walker well, drilled by the Indian Refining Company in sec. 9, T. 2 N., R. 2. W., Schuyler County, oil was reported in the Maquoketa shale at a depth of 751 feet, and about seven gallons of a light, brown oil are said to have been taken out. STRUCTURE General Statement The rocks in the area covered by this report lie practically horizon- tal, as far as can be seen by the casual observer. There are a few ex- posures where the beds are seen to be dipping (figs. 11 and 12), but the dip of such beds is probably due rather to the irregularity of the surface upon which they were deposited, than to any folding or tilting of the rocks since their deposition. However, if a single layer of rock, such as a bed of coal or limestone is traced over large areas, and its elevation above sea level determined at numerous points, it will be found higher at some places than at others. If enough elevations are determined, areas can be located in which the rocks have been arched up into low "anticlines" or "domes." Careful studies have shown that all of the rocks under this region lie approximately parallel to each other, so that if a single bed is found to be arched up, it is safe to assume that the under- lying rocks are arched up in the same manner and at the same place. Moreover, it has been shown that the larger part of the folding in this region took place after the deposition of the "Coal Measures" or Pennsylvanian rocks, so that No. 2 coal, for example, is probably folded about as much as the Niagaran limestone or other rocks several hundred feet below. It is true that the region oscillated above and below sea level several times during the deposition of these rocks, and erosion took place during periods of emergence so that the planes of contact between differ- 42 OIL INVESTIGATIONS Ist.drill hole Pig. 14. Diagrams showing conditions governing oil accumulation: A. In oil sands saturated with salt water; B. In oil sands partly saturated; C. In sands containing no water and only partly filled with oil. BROWN COUNTY 43 ent formation are in many cases quite irregular. The oscillations oc- curred without much deformation, however, so that each new series of beds was laid down nearly parallel to the beds below. This makes it safe to assume that anticlines existing in rocks at the surface also exist in any oil sands which may occur at some depth. Relation of Structure to Accumulation of Oil Where oil occurs in the rocks there are three principal factors which govern its accumulation into pools. These factors are : the exist- ence of a porous reservoir, the presence of impervious rocks above and below the porous reservoir, and the favorable rock structure. There are other factors which may apply in certain cases, but in the area under consideration the three enumerated are believed to be the most import- ant. Previous testing has shown that in places oil occurs in the rocks underlying western Illinois and that where conditions are favorable it has accumulated in commercial quantities. These favorable conditions are the presence of the porous Hoing sand, with the impervious Maquo- keta shale below it, and the relatively impervious Silurian or Devonian limestone or Devonian shale above it, and anticlinal or dome structures in the rocks. Most of the oil from the Colmar field has been obtained from a single lens of porous sandstone (the Hoing sand) lying on a structural terrace on the flanks of a large, elongate dome. Other lenses of sandstone higher up on the dome have produced smaller amounts of oil. The rock structure here was an all-important factor in determining the location of accumulations of oil. In an area where structures such as anticlines or domes are present, the localization of oil accumulations depends upon conditions which can be determined only by drilling, such as the lateral extent of the oil sand and the presence in it of salt water. If the sand underlies only a por- tion of an anticline or dome, then only that portion can be productive re- gardless of favorable structures. If the sand contains salt water as well as oil, the two will be arranged in the order of their specific gravities, with the oil above the water. If the sand is completely saturated with the two fluids, the oil will lie in the highest portions of the structure, that is, at the crest of the anticline or dome, while the water will occupy the synclines or basins. (See figure 1-iA.) If the sand is only partly saturated the water will still occupy the basins with the oil above it on the limbs or slope of the anticlines. If these slopes are flattened at any point, forming a terrace, the oil is very likely to lie on such a terrace. (See figure 14B.) The main productive area in the Colmar field lies on just such a terrace. If there is little or no water in the sand the oil will 44 OIL INVESTIGATIONS occupy the basins. (See figure 14C.) However, in western Illinois as far as is known at present the Hoing sand always contains considerable quantities of water, and oil when present has never been found in the synclines or basins. Extensive testing in the region surrounding the Col- mar field has shown the presence of several unconnected bodies of Hoing sand of considerable size, but in most cases they are well filled with salt water. A large area in the vicinity of Littleton in Schuyler County is underlain by Hoing sand and is arched into a well-developed dome. A well drilled almost at the center of the dome found large quantities of water in the sand with only a small showing of oil. Other wells found slight showings of oil, but all found salt water. It is evident that this sand body is completely saturated with salt water together with a very small amount of oil. Previous experience has shown that prospecting for oil in this region may well be confined to testing of known structures, if the structures can be determined by a study of surface rocks. Taking everything into consideration, it is believed that the first test wells should be located near the crests of the domes and anticlines. If the sand is found to be absent, further testing would not be advisable in the immediate vicinity. If the sand is present but is filled with salt water, further testing down the dip would not be advisable, for the lower portions of the sand are likely to be filled with water also unless a separate sand body is encountered. Just such a condition appears to exist in the Colmar field, however, where the main production is from a sand body on a terrace 60 feet lower than the crest of the dome ; yet many wells drilled high up on the dome found large quantities of water in the sand. If a first test reveals a good sand near the top of the structure, but barren of water or oil, other tests should be drilled farther down on the slope, especially on terraces. If a good sand is found on a terrace, but still barren of oil or water, final tests may be drilled in the synclines, where oil is likely to accumulate if the sand contains little or no water. Detailed Structure The detailed structure was worked out by obtaining the elevation of the seven key horizons described above. The most uniform and most reliable of all these horizons is No. 2 coal, and it was selected as the one most likely to show all details of structure. Its elevation above sea level was determined either by direct leveling or by computation from the ele- vations of the other key horizons, and a structure-contour map con- structed by drawing lines through all points of equal elevation. This map is reproduced in Plate I, and it reveals the structure as follows: BROWN COUNTY 45 In general the coal dips to the east, but it has a rolling surface upon which are developed small domes, anticlines, terraces, and synclines. The maximum elevation attained is 653 feet in sec. 5, T. 3 S., R. 4 W. (Fairmount Twp.), just over the line in Pike County. The coal in the southwestern portion of Brown County is high, with a decline to the east of 123 feet to an elevation of 530 near Illinois River. In the north- western portion of the county it is again high, rising to an elevation of 617 in sec. 29, T. 1 N., R. 4 W. (Pea Ridge Twp.), and decreasing to the east to an elevation of 516 in sec. 24, T. 1 N., R. 3 W. (Missouri Twp.). Outcrops are almost lacking in a broad belt across the central portion of the county so that it is impossible to predict the structure in that area. Covering most of T. 2 S., R. 3 W. (Elkhorn Twp.), and parts of adjoining townships is a broad terrace upon which lie three small domes. The terrace has an elevation of about 580 feet above sea level. A small dome covers most of sec. 6, T. 1 S., R. 4 W. (Lee Twp.), and sec. 1, T. 2 S., R. 4 W. (Buckhorn Twp.) At the apex of the dome in the NE. y A sec. 6, T. 2 S., R. 3 W. (Elkhorn Twp.), the coal has an elevation of 607 feet and is about 30 feet higher than to the north and east. To the south and west there is only a slight decline. In sec. 7, 8, 9, 17, and 18, T. 2 S., R. 3 W. (Elkhorn Twp.) is an irregular flat dome upon which the coal lies at an elevation of 600 feet or 30 feet higher than in the area to the north and east. A broad terrace at an elevation of 580 feet covers most of the southern half of T. 2 S., R. 3 W. (Elkhorn Twp.), with a slight doming in sees. 13, 24, and 25. The apex lies at 596 feet in section 13. To the east the rocks dip off rapidly, so that the apex of the dome rises about 50 feet. To the west there is first a gentle dip, then the rocks rise into a sharp anticline. Extending almost due north in sees. 16, 17, 20, 21, 32, and 33, T. 2 S., R. 4 W. (Buckhorn Twp.), is a sharp anticlinal nose on which the coal lies 50 to 60 feet higher than to the north, east, and west. The shape of this structure on the south has not been determined, since field work extended only a short distance south of the county line. The highest known point is in the NW. ]/\ sec. 5, T. 3 S., R. 4 W. (Fairmount Twp.), Pike County, where the coal lies 653 feet above sea level. To the west the coal dips steeply into a narrow syncline, while to the east it slopes gently toward the broad terrace in T. 2 S., R. 3 W. (Elkhorn Twp.) It is pos- sible that additional data in Pike County will modify this structure, and that the coal may rise even higher to the south. In T. 1 S., R. 2 W. (Cooperstown Twp.), is an area of uplift, but outcrops are very few, in this township, and it is impossible to outline the 46 OIL INVESTIGATIONS structure accurately. The data available suggest a broad dome with its apex in sections 27, 28, 32, 33, and 34, in which the coal lies 20 to 30 feet higher than in the area to the west, and 50 to 60 feet higher than in the area to the east. It slopes off gently to the north and south. In T. 1 N., R. 4 W. (Pea Ridge Twp.), is a dome with its apex lying in sections 20, 21, 28, and 29, at an elevation of 617 feet. It is 30 feet higher than to the east, south, and west. To the northeast it flat- tens out into a broad terrace, covering sections 2, 3, 9, 10, 15, and 16 at an elevation of 590 to 600 feet. In sections 13 and 14 of the same town- ship is a slight dome arising about 20 feet above the surrounding terri- tory, and sloping off into a low, narrow anticline to the northeast in sees. 5, 6, 7, and 8, T. 1 N., R. 3 W. (Missouri Twp.) A narrow strip across the northeast corner of the county, covering parts of Missouri and Ripley townships, was studied in 1914 by Morse and Rich. 1 The structural relations suggested by them have been slightly modified by new data, obtained in the course of the present work, but no important changes need be made. A dome exists in sees. 1, 2, 11, and 12, T. 1 N., R. 3 W. (Missouri Twp.), as indicated by their work, with a large syncline to the southeast. The broad Ripley dome in T. 1 N., R. 2 W. (Woodstock, Schuyler County, and Ripley, Brown County), is best interpreted as a terrace, since the new data indicates that the con- tour lines do not close around the south end. A small synclinal basin in sees. 8, 9, 16, and 17, T. 1 S., R. 3 W. (Mt. Sterling Twp.), completes the list of structures brought out by the contour map. LOCALITIES PREVIOUSLY TESTED Several attempts have been made to discover oil in the area covered by this report, and five wells have been drilled. The first is said to have been drilled 40 or 50 years ago in sec. 24 or 25, T. 2 S., R. 3 W. (Elkhorn Twp.), by local people, but no data is available as to the depth of the well or the result of the test. The next test well was drilled in 1914 on the J. and L. Parke farm in sec. 25, T. 1 S., R. 2 W. (Coopers- town Twp.), by the Pure Oil Operating Company. No sand was found at the base of the Niagaran limestone, and the well was abandoned. The log of the well is a follows : 1 Morse, Wm. C, and Kay, Fred H., The area south of Colmar oil field: 111. State Geol. Survey Bull. 31, pp. 8-36, 1915. BROWN COUNTY 47 Log of J. and L. Parke well, sec. 25 T. 1 S., R. 2 W. Surface elevation — 648 feet Thickness Depth Feet Feet Sand and gravel (glacial drift) 125 125 Limestone (Salem) 20 145 Slate and shale (Warsaw and Keokuk) 80 225 Limestone (Keokuk and Burlington) 227 452 Slate (Kinderhook and Upper Devonian) 195 647 Limestone (Devonian and Niagaran) 67 714 Total depth 714 Another well was drilled in 1914 on the Sale Johnson farm in the NE. % sec. 24, T. 2 S., R. 5 W., almost on the line between Brown and Adams counties. Here also the sand was absent and the well was dry. The log of this well with formation names inserted in parentheses by the author is reported by Mr. W. E. Lancaster, as follows : Log of Sale Johnson well, NE. % sec. 2k, T. 2 8., R. 5 W. Surface elevation — 609 feet Clay and gravel Gray lime (strong flow of water) (Salem) Blue shale, with thin streak of shells (Warsaw and Keokuk) White lime (strong flow of water) (Keokuk and Burlington) Green shale ") Blue shale L( Kinderhook and Upper Devonian) Brown shale I Gray lime cap rock (Devonian and Niagaran) Blue shale ( Maquoketa ) Gray shale showing streaks of sand shells (Maquoketa).... Total depth 630 Following this the Pea Ridge Oil Company drilled two wells (in 1915 and 1916) on the Thomas May farm in sees. 20 and 21', T. 1 N., R. 4 W. (Pea Ridge Twp.) The first was drilled in the N. j/ 2 SW. % section 21 and penetrated two feet of good sand with a slight show of oil, but with much salt water. The second well was drilled about half a mile southwest of the first in the SE. l/± section 20 and penetrated 12 feet of sand but was likewise dry. The logs of the two wells are as follows: Thickness Depth Feet Feet 14 14 24 38 90 128 220 348 25 373 40 413 120 533 30 563 27 590 40 630 48 OIL INVESTIGATIONS Log of May well No. 1, N. y 2 8W. % sec. 21, T. 1 N., R. 4 W. (Pea Ridge Twp.) Elevation — 620 feet Thickness Depth Feet Feet Loam clay, soapstone 14 14 Coal (No. 2) 2 16 Soapstone ) 9 25 Lime shale } (Pottsville) R 39 Lime rock ) 5 80 „ . . > (St. LOUiS) o/J fyr Green shale j 36 75 Lime rock (Salem, Warsaw, Keokuk and Burlington) 290 370 Green shale ] 140 510 Brown shale UKinderhook and Upper Devonian) 15 525 Light shale J 25 550 Lime rock (Devonian or Niagaran) 10 560 Sand (Hoing) .'.'. 2 562 Gray shale (Maquoketa) 20% 582% Total depth 582% Show of oil in the sand, but salt water rose 200 feet in the hole above the sand. Log of May well No. 2, SE. V^ sec. 20, T. 1 N., R. k W. (Pea Ridge Twp.) , Elevation 635 feet Dirt and shale to coal 18 18 Coal streaked with shale (No. 2) . . , 8 26 Shale ] 12 38 Lime rock j, Pottsville 2 40 Hard pan J 7 47 Lime rock "j 3 50 Broken lime rock 8 58 Blue lime rock , Broken lime rock Solid lime rock Broken lime rock Solid lime rock Broken lime rock Solid lime rock Water-bearing lime rock Solid lime rock Shale with ore Gray shale Shale Lighter shale 4 62 ("First lime" St. 8 70 Louis, Salem, Warsaw, 20 90 .Keokuk, and Burling- 20 110 ton formations) 10 120 20 140 70 210 30 240 150 390 3 393 57 450 (Kinderhook and Upper Devonian) 90 540 13 553 Lime rock (Devonian and Niagaran) 22 575 Sand (Hoing) 12 587 Total depth 587 BROWN COUNTY 49 RECOMMENDATIONS Future testing of the localities here mentioned should take into full account the factors previously described which govern the accumulation of oil. Since the. oil sand is absent over large areas drilling must be more uncertain than is ordinarily the case, in spite of the existence of favorable geological structures. The shallow depth at which oil may be expected, however, makes drilling comparatively inexpensive and a dry hole does not mean such a loss as in the case of deep drilling. In gen- eral, prospecting should be carried out with the principles stated in the section on relation of structure to oil accumulation as a guide. 1. Under ordinary circumstances the dome in sees. 20, 21, 27, 28, and 29, T. 1 N., R. 4 W. (Pea Ridge Twp.), would be recommended for thorough testing. However, both of the wells drilled by the Pea Ridge Oil and Gas Company lie on the structure. No. 2 coal lies 8 feet lower in well No. 1 than in well No. 2, but the elevation of the top of the oil sand is the same in the two wells. These wells show that the oil sand is thickening to the west and south. Since it contained only salt water, any accumulation of oil in the same sand body must lie up the dip. Unfortunately the field data is insufficient to show the structure to the west of these two wells. It is evident that if the coal rises higher it must be to the west or southwest, for it is dipping to the north, east, and south. The chances are good that a well drilled half a mile to a mile southwest of Thomas May No. 2 would penetrate the sand well up the dip. 2. A long terrace lies to the northeast of the May wells, in sees. 11, 12, 13, and 14, T. 1 N., R. 4 W., (Pea Ridge Twp.) and sees. 5, 7, 8, and 18, T. 1 N., R. 3 W. (Missouri Twp.) It is unlikely that the sand body extends very far to the east of May No. 1 since it was there only two feet thick. A successful test on this terrace would depend upon the presence of a sand lens entirely separated from the one to the southwest, and lying at a lower elevation. If the generalization referred to in the section on the relation of structure to accumulation of oil can be relied upon, this terrace should be the logical place to expect to find such a lens. The best location for a test is probably in the east half of sec. 13, T. 1 N.. R. 4 W. 3. The dome covering parts of sees. 1, 2, 11, and 12, T. 1 N., R. 3 W., extends east into Schuyler County where it has already been thoroughly tested by three wells of the Ohio Oil Company. No sand was found in any of the three wells, which therefore discredit the dome. 4. There is an elevated area in the southern half of T. 1 S., R. 2 W. (Cooperstown Twp.), which can not be accurately outlined owing to 50 OIL INVESTIGATIONS lack of data. The well drilled in 1914 on the Parke farm is located about 2y 2 miles northeast of the highest part of this structure, as far as the available data indicates. Since the Parke well failed to find the sand, testing of this structure should remain until the more favorable areas have been prospected. The best location for such a test is in the NE. *4 sec. 33, T. 1 S., R. 2 W. 5. Perhaps the most attractive-looking structure in the county is the broad terrace in T. 2 S., R. 3 W. (Elkhorn Twp.) There have been no wells drilled within 8 or 10 miles except the old well drilled 40 or 50 years ago in section 24 or 25, and concerning which little is known. There is a large area over which the structure is favorable, and if it could be demonstrated that the oil sand is present, very thorough prospecting would be advisable. Since there is no information as to the distribution of the oil sand, the first test should be located on the highest point on the structure which is in the NE. y sec. 6, T. 2 S., R. 3 W. Another area almost as high crosses sections 7, 8, 9, 17, and 18. A test of this area might well be located in the S. y 2 section 8 or the NW. J4 section 17. To the southeast of these two areas lies the main portion of the terrace about 20 feet lower, with its general surface at an elevation of 680 feet above sea level. In the SW. % section 13, however, it rises to an elevation of 596 feet, then dips rapidly to the north and northeast. An initial test would best be located in the NW. ^4 section 24 or the NE. V^ section 23. If early tests on the higher portions of the structure prove unproductive, the broad portion of the terrace in sections 21, 22, 23, 24, 25, 26, and 27 should be tested later. 6. The highest structure in the county and for that reason one of the most favorable, is the anticline in the south half of T. 2 S., R. 4 W. (Buckhorn Twp.), and extending over the line into Pike County. Here No. 2 coal rises more than 50 feet in a distance of only about a mile. On the crest of the anticline it lies at an elevation of 653 feet and slopes off to 600 feet in about a mile to the west, to 590 in about 3J^ miles to the east, and to 590 in about 6 miles to the north, thus forming an anticlinal nose to the north. The dry hole drilled on the Sale Johnson farm in 1914 lies almost at the bottom of a syncline, and is about three miles distant from the crest of the anticline. The extension of this structure to the south will no doubt be modified by further mapping, but it has been sufficiently outlined to make testing desirable. At present the best lo- cation for a test appears to be in the S. y 2 sec. 32, T. 2 S., R. 4 W. (Buckhorn Twp.), Brown County, or the N. y 2 sec. 5, T. 3 S., R. 4 W. (Fairmount Twp.), Pike County, and further testing should probably extend to the northeast. GOODHOPE AND LA HARPE QUADRANGLES By Merle L. Nebel OUTLINE PAGE Introduction 51 Acknowledgments 52 Strata outcropping at the surface 52 Strata penetrated in drilling. 53 Possible oil-bearing horizons ....... 59 Relation of accumulation to folds in the oil-bearing bed 62 Structure 63 General discussion , 63 Detailed descriptions 64 Localities already tested 66 Gas in the glacial drift 66 ILLUSTRATIONS PLATES II. Map of Goodhope quadrangle showing structural contours based upon the elevation of No. 2 coal (red) and upon the elevation of the Burlington limestone (black) above sea level 62 III. Map of La Harpe quadrangle showing structural contours based upon the elevation of No. 2 coal (red) and upon the elevation of the Burlington limestone (black) above sea level 66 FIGUKE 15. Graphic section showing the succession of strata underlying Good- hope and La Harpe quadrangles 54 INTRODUCTION This report has been prepared in response to numerous requests for information concerning the structure of the area described in rela- tion to possible occurrences of oil or gas, and does not attempt to de- scribe the geology in detail. The latter information will be contained in a more complete report in the course of preparation which will be pub- lished later. The field work upon which both reports are based was done in the summer and fall months of 1917. Although a few wells have been drilled in the area in search for oil, it has by no means been thoroughly prospected. The oil sand from which it is most reasonable to expect to obtain oil, the Hoing sand of the Colmar field, is known to be absent in certain parts of the Goodhope- La Harpe region, and it is probably present only as isolated lenses or (51) 52 OIL INVESTIGATIONS sand bodies in scattered localities. The geologist can not predict the presence of this sand in advance of the drill, and the most that he at- tempts to do is to eliminate as much of the chance as possible by point- ing out areas in which the rocks are arched up into domes or anticlines. Here accumulation can take place if the oil sand and certain other con- ditions are present, and if water saturation is complete enough to hold the oil or gas in the upward folds. It would be wise to confine testing to areas in which favorable structures have been found, since the natural hazards of prospecting can in that way be reduced. Although no one can guarantee oil at a given location, nevertheless valuable services can be rendered by limiting exploration to small areas. Acknowledgments In his field work in the La Harpe quadrangle and a portion of the Goodhope quadrangle the writer was assisted by Marvin Weller. An introduction to the geology of the region was given by T. E. Savage in a short reconnaissance trip. Information concerning coal and other strata penetrated by wells was freely furnished by most of the residents. The assistance of John W. Coghill, Jr., of Roseville, was especially val- uable in this connection. STRATA OUTCROPPING AT THE SURFACE In the Goodhope quadrangle only rocks of the Pennsylvanian ("Coal Measures") system outcrop. In the La Harpe quadrangle both Pennsylvanian and the underlying Mississippian rocks are found. A composite section made up from a study of many outcrops, and showing the character and thickness of the various strata is as follows : Composite section of Pennsylvanian and Mississippian rocks in the Goodhope* La Harpe region Thickness Character of strata Feet Pleistocene and Recent Sand, gravel, glacial till (boulder clay) and soil 1 to 220 Pennsylvanian system Carbondale formation Shale, limestone, and coal, to the base of No. 2 coal 2 to 85 Pottsville formation Shale, sandstone, limestone, and coal (including No. 1 coal).. 20 to 125 Mississippian system St. Louis limestone Brecciated limestone and dolomite. 20 to 35 GOODHOPE AND LA HARPE QUADRANGLES 53 Composite section of Pennsylvania and Mississippian rocks in the Goodhope- LaHarpe region — Concluded Thickness Feet Salem (Spergen) limestone Limestone and calcareous sandstone 6 to 12 "Warsaw formation Shale and limestone 30 to 40 Keokuk limestone Limestone and chert; only a few feet exposed in the area; normal thickness 50 to 100 Burlington limestone Limestone and chert 150 to 200 Of the rocks shown in this section, the Burlington limestone out- crops only in the northern and western portions of the La Harpe quad- rangle, and the Keokuk limestone only at a few points in the western portion of the same quadrangle. Rocks of the Warsaw, Salem, and St. Louis formations outcrop only in the southwestern portion of the La Harpe quadrangle. Rocks of the Pottsville and Carbondale formations outcrop in the eastern half of the La Harpe quadrangle and at scattered localities throughout the Goodhope quadrangle, STRATA PENETRATED IN DRILLING The strata penetrated in drilling for oil include those known from outcrops, described above, and in addition other strata of the Missis- sippian system and shales, limestone, and dolomites of the Devonian and Silurian systems which lie above the horizon of the Hoing sand. Im- mediately below the Burlington limestone is a thick shale bed, known as the Kinderhook shale, which lies at the base of the Mississippian system. It varies in thickness from about 85 to 125 feet. Lying un- conformably below it is the Sweetland Creek shale of Upper Devonian age which varies in thickness from 100 to 150 feet. Below this is a gray, non-magnesian limestone of late Middle or Upper Devonian age, usually referred to as the Devonian limestone. It is not always possible in drilling to dstinguish it from the underlying Niagaran limestone, but it is known to have a thickness of about 40 to 80 feet or more. Lying unconformably below the Devonian limestone is a porous dolomite of Silurian age usually referred to simply as the Niagaran dolomite. A few wells have been drilled in which this dolomite proved to be entirely missing, but it is usually present in thicknesses varying from 8 or 1 feet to 80 feet or more. The Hoing sand, when present, lies just at the base of this dolomite. Deep wells which may be drilled to test the so-called "Trenton limestone" ( Galena- Platteville) will pass through 180 to 200 54 OIL INVESTIGATIONS rO -100 200 300 400 500 600 700 800 LEGEND g.^— /o—i Drift Sand Shale Limestone • 1 • . I . . I".- '■ - y - • ; i 1 [' •■ l • • [ • ' Sandy limestone 900 1000 Chert Coal 8: 1 fei B 3 o 1 Pleistocene Carbondale Pottsville St. Louis Salem Warsaw Keokuk Burlington Kinderhook Sweetland Creek Devonian e — \ .A— — <^ \ o ^ Niagaran Horizon of Hoing Sand IE ^ Ei is: 5S Maquoketa Pig. 15. Graphic section showing the succession of strata underlying Goodhope and LaHarpe quadrangles. GOODHOPE AND LA HARPE QUADRANGLES 55 feet of shale below the Niagaran. This is the Maquoketa shale of the Ordovician system. The detailed succession of strata may be understood best by re- ferring to the accompanying graphic section (fig. 15) and the logs of wells drilled in the area which are given below. Two of these (Strong- hurst and Bushnell) are water wells and the other two were drilled in search of oil. Log of well in the town of Stronghurst in the SE. 14 NW. *4 NE. % sec. 25. T. 9 N., R. 5 W., Henderson County (Interpreted from driller's log by T. E. Savage) Altitude of surface— 665 feet Thickness Depth Feet Feet Quaternary Soil and drift 150 150 Kinderhook and Upper Devonian Shale, gray 165 315 Devonian and Silurian Limestone 105 420 Ordovician Maquoketa Shale ... 165 585 Galena-Platteville Limestone, gray 200 785 Limestone, brown 15 800 Limestone, gray 60 860 St. Peter Sandstone 171 1031 Shale, white 25 1056 Prairie du Chien Limestone, white 10 1066 Shale, white 5 1071 Limestone, white 24 1095 Sandstone, white 20 1115 Limestone 50 1165 Shale 5 1170 Limestone 105 1275 Sandstone 5 1280 Limestone 25 1305 Cambrian - St. Croix or Potsdam Sandstone 296 1601 56 OIL INVESTIGATIONS Log of well in the city of Bushnell, near the center of sec. 33, T. 7 N., R. 1 W., McDonough County (Compiled from study of drill cuttings compared with driller's log) Altitude of surface — 651 feet Thickness Depth Feet Feet Quaternary Clay, yellow, and loam, black 40 40 Clay, blue 60 100 Sand, water 10 110 Pennsylvanian Pottsville 1. Shale, gray 20(?) 130 Mississippian and Upper Devonian Warsaw 2. Shale, gray — 6(?) 136 Keokuk-Burlington 3. Limestone, white, fragments of chert numerous; frag- ment of crinoid stem noted 50 186 4. Same, with crystals of calcite 66 252 5. Limestone, white to light gray, cherty, with numer- ous crinoid stems and crystals of calcite 78 320 6. Same, with rounded quartz pebbles and basic igneous pebbles from the surface 15 335 7. Chert, white, with some limestone and calcite; crin- oid stem noted 35 370 Kinderhook and Devonian 8. Shale, blue-green, fine texture, thin beds, with an occasional fragment of chert, pyritiferous 39 409 9. Same 31 440 10. Shale, dark brown, hard, thin bedded, micaceous, highly bituminous. When thoroughly ignited will burn 170 610 11. Shale, gray-green, fine texture, thin bedded, not cal- careous 20 630 Silurian Niagaran 12. Limestone, gray, very argillaceous, soft, containing fragments of brachiopod shells 20 650 13. Limestone, gray, powdered by drill; slightly argil- laceous 30 680 14. Limestone, with a few fragments of gray-green shale;. numerous crinoid stems 15 695 15. Limestone, like the last with some chert and iron rust; fragments of brachiopod shells noted 15 710 16. Dolomite, straw colored, finely crystalline with al- most an equal amount of minute fragments of white chert. Some steel gray shale, small crystals of pyrite, and an occasional quartz grain present 15 725 GOODHOPE AND LA HARP E QUADRANGLES 57 Log of well in the city of Bushnell — Concluded Thickness Depth Feet Feet 17. Dolomite, white, finely crystalline, powdered, with very fine fragments of white chert; few sand grains 7 732 18. Sand, white, dolomitic, pyritiferous, sand gfrains slightly rounded, clear quartz, some shale present 8 740 Ordovician Maquoketa 19. Shale, grayish-green, fine texture 7 747 20. Shale, brownish-gray, with a small amount of gray, fine grained, dolomite 38 785 21. Shale, dark gray, fine grained, thin bedded, arena- ceous, with gray dolomite 36 821 22. Shale and dolomite, like the preceding. This sam- ple was labeled by the driller "888 to 892 notice in particular". There is however, nothing exceptional about the sample 71 892 23. Sandstone, gray, argillaceous, dolomitic, very fine grained, some pieces of chert and coal 11 903 Galena-Platteville 24. Dolomite, dark straw color, fine grained; powdered by drill. Very little reaction with cold dilute acid which becomes brisk when heated 17 920 25. Same 63 983 26. Same only somewhat lighter in color 57 1040 27. Same 30 1070 28. Same 30 1100 29. Dolomite, light brown, fine grained, with some very small bits of dark shale 40 1140 St. Peter 30. Sandstone, white, with medium sized rounded, clear, quartz grains. Cement dolomitic 160 1300 31. Sandstone, flesh color, very fine grained. Cement dolomitic 50 1350 Log of Parrish well in NW. *4 NW. % sec. Sit, T. 9 N., R. 3 W., (Ellison Twp.) Warren County Altitude of surface — 752 feet Quaternary Soil and clay (probably loess) Clay, blue Shale or clay Sand Pennsylvanian Pottsville Shale Thickness Depth Feet Feet 25 25 10 35 5 40 2 42 28 70 58 OIL INVESTIGATIONS Log of Parrish well — Concluded Thickness Depth Feet Feet Sand 4 74 Shale, blue 36 110 Limestone 6 116 Shale, blue 46 162 Limestone 2 164 Shale 5 169 Mississippian Burlington Limestone 20 189 Shale 2 191 Limestone 131 322 Kinderhook Shale, light. . .' 118 440 Devonian Upper Devonian (Sweetland Creek) Shale, brown to black 10 450 Shale, drab with spores of Sporangites huronense 105 555 Devonian and Silurian Limestone, gray, dolomitic 10 565 Limestone, gray, non-dolomitic 35 600 Limestone, dark 20 620 Dolomite, gray .. 42 662 Ordovician Maquoketa Shale, light 12 674 Log of Gochenour well near center NE. y± sec. 3, T. 6 N., B. 5 W., (Fountain Green Twp.) Hancock County (Compiled from study of drill cuttings and driller's log) Altitude of surface— 660 feet Thickness Depth Feet Feet Quaternary Soil, clay and gravel 30 30 Mississippian St. Louis, Salem, and Warsaw Limestone and shale 85 115 Keokuk and Burlington Limestone, leached, with chert fragments 45 160 Limestone, white, crystalline, with much chert 90 250 Limestone, white, crystalline, with little chert 75 325 Limestone, with some greenish shale 30 355 Kinderhook Shale, greenish to gray 45 400 Shale, greenish to gray, crystalline 80 480 GOODHOPE AND LAHARPE QUADRANGLES 59 Log of Gochenour well — Concluded Devonian Upper Devonian (Sweetland Creek) Shale, greenish, with dark fragments, the latter contain- ing numerous spores of Sporangites liuronense 100 580 Devonian and Silurian Dolomite and limestone, gray, subcrystalline, with pyrite 40 620 Limestone, gray, with chert fragments, mostly fine grained 110 730 Dolomite, gray to drab, with small quartz sand grains.. 15 745 Ordovician Maquoketa Shale, bluish gray 10 755 POSSIBLE OIL-BEARING HORIZONS There are four possible oil-bearing horizons in the rocks under- lying the Goodhope-La Harpe region. These are, in order of depth, the Pottsville sandstone, the Niagaran dolomite (Silurian), the Hoing sand (at base of Niagaran), and the Galena-Platteville limestone or dolomite. Large quantities of oil have been produced from Pottsville sand- stones in the northern part of the main oil fields in the southeastern part of the State. There, however, the Pottsville formation is thick and con- tains thick sandstone beds which are persistent over comparatively large areas. In the Goodhope-La Harpe region thick sandstones in the Potts- ville are the exception rather than the rule. The thickest known is that which outcrops on Cedar Creek at the northeast corner of the Goodhope quadrangle, where it has a maximum thickness of about 30 feet. Thick- nesses of 50 to 75 feet are reported in some wells, but undoubtedly in- clude a considerable thickness of shale. There has been no production of oil from the Pottsville from western Illinois, but oil is reported to have been encountered in a few wells drilled into it in search for water. Mr. John Anderson states that a well was drilled on his farm near the NW. corner SW. ]/ A sec. 12, T. 8 N. R. 2 W. (Swan Twp.), Warren County, in which a thick black oil was encountered in sandstone at a depth of 75 or 80 feet (top of sandstone at 35 feet). A quantity estimated at several barrels is said to have flowed out of the well, but this was finally cased off, and fresh water struck at 90 feet. Two wells drilled in sees. 17 and 18, T. 9 N., R. 3 W. (Ellison Twp.), Warren County, are said to have encountered oil at depths of 120 and 100 feet, respectively. However, no considerable production of oil is to be expected from the Pottsville sandstone in this region, owing to its shallow depth, its small lateral ex- tent, and the fact that it outcrops at numerous places, both at the surface and under the glacial drift. Pottsville rocks underlie all of the Good- hope quadrangle and approximately the eastern half of the La Harpe 60 OIL INVESTIGATIONS quadrangle, but it is very unlikely that sandstones are present in the Potts- ville under all of this area. The Niagaran dolomite is very porous and frequently contains small quantities of gas and oil, but has never furnished oil in commercial quantities. Gas has been produced from the Niagaran in the Pike County field for many years, and small amounts of heavy, black oil have been reported in the same area. Throughout western Illinois gas is frequently encountered in wells which penetrate the Niagaran. In Hen- derson County, in the vicinity of Media, gas and showings of oil were encountered in several wells, although no production has been secured. A rather unusual feature of these wells is that the gas and oil seem to lie in the upper part of the "second lime" ; that is, in the Devonian lime- stone, rather than the Niagaran dolomite. The data are insufficient to determine the horizon exactly, however. Neither the Devonian lime- stone nor the Niagaran dolomite are considered so promising for oil pro- duction as is the Hoing sand. The Hoing sand is not a continuous bed, but consists of isolated lenses of a porous, white sandstone which occur at the base of the Niagaran dolomite, and immediately overlying the Maquoketa shale. Prospecting for oil in this sand is therefore unusually hazardous, since the presence of the sand can not be predicted in advance of drilling. It is probably absent over a considerable portion of the Goodhope-La Harpe area, and a search for oil must therefore in large part consist in a search for bodies of the sand. There are only two localities in which the sand is known to occur. One of these is the vicinity of Bushnell in the southeastern portion of the Goodhope quadrangle. In the new city well there, drilled in 1915 the driller reported about 15 feet of sandstone at the base of the Niagaran dolomite. Samples of drill cuttings from the well were examined by members of the Survey staff and show that such a sandstone is present. The lower eight feet consists of white, quartz sand, and the seven feet above this contains a considerable pro- portion of sand. The second locality in which sand was reported at the base of the Niagaran is southeast of La Harpe in the southwestern por- tion of the La Harpe quadrangle. Samples of the drill cuttings from a well drilled on the Gochenour farm in the NE. % sec. 3, T. 6 N., R. 5 W. (Fountain Green Twp.), Hancock County, were examined at the Sur- vey office, and it was found that the basal 15 feet of the Niagaran dolomite contained a considerable amount of quartz sand grains. An- other well was drilled on the Gills farm in sec. 8, T. 6 N., R. 3 W. (Emmet Twp.), and although no log of the well is available, Mr. Gills reports that about 20 feet of sand was found at the base of the Niagaran, GOODHOPE AND LA HARPE QUADRANGLES 61 with a showing of gas. It is impossible to state whether this was a clean quartz sand, or the ground-up bits of dolomite which are easily con- fused with the quartz sand. Another well in the SW. % NW. Ya sec. 18, T. 6 N., R. 2 W. (Macomb Twp.), reported four feet of good sand with a showing of oil. Although a well may penetrate to the Maquoketa shale without finding the Hoing sand, it does not necessarily discredit the territory immediately surrounding it, for the known lenses of sand are small in areal extent and one of two adjoining wells may find a good sand and the other miss it entirely. There are numerous instances of this sort in the Colmar pool, where two or more separate lenses occur cutting across the Colmar dome and the Lamoine terrace. 1 Therefore an area where the rock structure is favorable for the accumulation of oil or gas can not be thoroughly tested and condemned on the basis of absence of the sand in a single well. Sufficient drilling must be done to demonstrate the general absence of the sand throughout the favorable area before the structure can be said to be fairly tested. There are two possible oil-producing horizons below the Hoing sand, but neither is regarded as likely to be productive in this region. The first is the Maquoketa shale, in which showings of oil have been reported in western Illinois. In the Indian Refining Company's well on the Walker farm in sec. 9, T. 2 N., R. 2 W. (Buena Vista Twp.), Schuyler County, oil was reported at a depth of 751 feet, about 74 feet below the top of the Maquoketa, and several gallons are said to have been taken from the well. The second horizon below the Hoing sand which might prove productive is the Galena-Platteville limestone below the Maquoketa. This rock is frequently dolomitic and porous, and showings of oil have been reported from it. It occupies about the same position in the geological column as the so-called "Trenton" of south- eastern Illinois from which a small quantity of oil is being produced. The Trenton limestone of Ohio and Indiana has been the source of large quantities of oil. There is no assurance that this horizon will prove pro- ductive in western Illinois, but an occasional well should be drilled through it where the geologic structure is favorable, in order to test the region thoroughly. It is the oldest known rock in this area in which any oil may reasonably be expected, and since it can be reached at a depth of not over 1,000 feet, testing should be relatively simple and inexpensive. 1 Kay, F. H., and Morse, W. C, The Colmar oil field: 111. State Geol. Survey Bull. 31, pp. 42-43. 62 OIL INVESTIGATIONS RELATION OF ACCUMULATION TO FOLDS IN THE OIL- BEARING BED Thorough studies of oil and gas occurrence throughout the world have demonstrated beyond question the importance of rock structure in determining the accumulation of these substances. Although one can by no means state that all oil occurs in anticlines or domes, previous experience and careful studies of known oil pools in Illinois have shown that the proper conditions for accumulation in the area under discus- sion are most likely to be met with at the crests of folds such as anti- clines or domes, and that such places should be tested first in new ter- ritory. There are three principal conditions governing accumulation. They are as follows : 1. The presence of a porous bed, such as a sandstone or cavernous limestone to serve as a reservoir. 2. An impervious cover, such as shale or other fine grained rock to prevent the escape of the oil or gas. 3. Folding in the rocks by which are produced dips along which the oil and gas can migrate and segregate into pools. The first condition may be met in this region by any one of the beds described above under the heading "Possible oil-bearing horizons." The second is met by the Maquoketa shale lying above the Galena-Platteville limestone, the Kinderhook and Upper Devonian shales above the Niagaran dolomite and the Hoing sand, and the Pennsylvanian shales above the Pottsville sandstone. The third condition, that of folding to produce favorable geological structure, is met at certain localities, and it is the purpose of this report to point out the areas in which favorable structures exist. The accumulation of oil in a given structure is to a considerable degree dependent upon the presence and amount of salt water in the sand. The productive oil fields of Illinois are in the main surrounded by barren areas in which the sand contains salt water. Where the sand is saturated, the oil lies near the crest of the anticlines or domes, with the gas, if any, above it (fig. 14 A). Where the sand is only partly saturated the oil lies farther down the sides of the folds, at the upper surface of the water, and the crests may be dry (fig. 14 B). A rather common mode of occurrence is on flattened terraces on the sides of a fold such as is shown in figure 14 B. If water is absent from the sand, the oil may occur in the troughs or synclines (fig. 14 C). This mode of occurence is comparatively rare and prospecting should be confined to the domes, anticlines and terraces, unless it is demonstrated that the sands contain no water. ■ .-;**' . ' *g2& i\^M S& .a&ll.i | ■' . . - -.«?■"*■" '""~ A, »^---. . • ■ GOODHOPE AND LA HARP E QUADRANGLES 63 STRUCTURE General Discussion The geologic structure of a given area can be determined best by a study of rock outcrops supplemented by information obtained from well logs. If a definite bed outcrops over large areas and can be readily identified and traced from place to place it is a comparatively simple matter to determine its altitude above sea level at numerous localities. If the same bed can be recognized in well logs, its altitude can be obtained over considerable areas in which it does not outcrop. In the Goodhope- La Harpe area No. 2 coal is just such a "key" bed. Its altitude has been determined at numerous points in the area which it underlies and structural contour maps have been prepared by drawing lines through points of equal elevation. (See Plates II and III, red contours.) If it can be assumed that the key bed lies parallel to the oil sands several hundred feet below, then the structure shown by that bed can be said to represent faithfully the structure of the oil sands. However, this is not strictly true for the area under consideration, as is shown by the fol- lowing discussion. The greater portion of the State of Illinois occupies a large struct- ural basin or syncline with its western border roughly parallel to the Mississippi River. 1 Superimposed upon this large synclinal structure are numerous small structures such as anticlines, domes, terraces, and synclines. Over this large basin structural disturbances took place in the intervals between the deposition of successive formations, and the beds now exposed at the surface do not necessarily show structure parallel to that of the underlying rocks. This is best brought out by a study of some deeply buried bed or horizon which can be recognized in well logs. In the Goodhope-La Harpe area the most satisfactory horizon for this pur- pose is the base of the Burlington limestone. Accordingly the altitude of this key horizon was determined wherever wells could be found which penetrated deeply enough, and structural contour maps were constructed just as in the case of the coal. The only difference is that the points are fewer and are more widely scattered, so that the structure is neces- sarily generalized, and small details are not shown. This structure is shown by black contours on the maps (Plates II and III). A careful study of the two sets of contours demonstrates the lack of parrallelism between the two key horizons. They both have the same general direction of dip, namely, to the east and south toward the center of the large Illinois basin, but the Burlington limestone dips much more A Geologic Map of Illinois: State Geol. Survey, 1917. 64 OIL INVESTIGATIONS steeply. At a point near the center of the west edge of the Goodhope quadrangle the base of the Burlington limestone lies at an elevation of about 500 feet, while near the center of the east edge of the same quadrangle, 12 miles away, it has an elevation of only 235 feet. The decrease amounts to 265 feet, or 22 feet per mile, while the elevation of No. 2 coal decreases only about 87 feet in the same distance, or 7% feet per mile. In the La Harpe quadrangle the elevation of the base of the Burlington limestone decreases 170 feet from the central to the southern portion, while the elevation of No. 2 coal decreases only 71 feet in the same distance. The ideal key horizon to determine structure which may be used in prospecting for oil is the upper surface of the oil sand itself. Lacking sufficient data concerning the sand, the next best key horizon is that approaching nearest to the oil sand in depth. In the Goodhope-La Harpe area this is the base of the Burlington limestone, and the struct- ure shown by this horizon should be considered first in selecting loca- tions for drilling. This may be supplemented by testing the structures shown by the coal if the divergence between the two horizons is taken into account. The effect of this divergence as the depth increases is to displace the apex of the structure in the direction in which the interval between the beds is increasing. Therefore a test well in order to strike the oil sand at the apex of a dome must not be drilled at the apex indicated by the coal structure, but to one side or the other. The proper place to test the structures shown by the coal in this area is pointed out in the description of individual structures which follows. Detailed Descriptions The principal structural feature shown by the contours on the base of the Burlington limestone is a dome covering a large area in the north half of the La Harpe Quadrangle. The apex lies near Stronghurst, where the Burlington rises to an altitude of 603 feet. To the west it appears to have a steep dip to an elevation of 390 feet, but this is based upon the log of one well in the SW. Y A of sec. 28, T. 9 N., R. 5 W. (Stronghurst Twp.), which passed through limestone from 90 to 250 feet. If this is the Burlington limestone, as the driller called it, its base lies at an elevation of about 390 feet. To the south of Stronghurst the limestone dips off fairly uniformly to an elevation of 300 feet south of La Harpe. To the east it has a gentle dip across the La Harpe quad- rangle, which becomes steeper from west to east across the Goodhope quadrangle and reaches a minimum elevation of 235 feet in sec. 22, T. 8 N., R. 1 W. (Greenbush Twp.) To the north of Stronghurst the GOODHOPE AND LAHARPE QUADRANGLES 65 dome is incompletely defined. There is a dip of over 50 feet per mile to the northeast toward Media. There is an area of 100 to 150 square miles lying on the gentle east and southeast slope of the dome in which there have been no wells drilled deep enough to test out the horizon of the Hoing sand. If the sand is present in any portion of this area the geological conditions are favorable for the accumulation of oil, but the presence or absence of the sand can be demonstrated only by drilling. The first tests should be drilled well up on the structure, within the area bounded by the 550- foot contour line; that is, in sees. 31 and 32, T. 9 N., R. 4 W. (Strong- hurst Twp.), in sees. 25, 26, 35, 36, T. 9 N., R. 5 W. (Stronghurst Twp.), and in sees. 5, 6, 7, 8, 9, T. 8 N., R. 4 W. (Raritan Twp.) Further drilling should be extended to the area included within the 500- foot contour line, in which case it would seem advisable to locate the first test in sec. 33, T. 8 N., R. 3 W. Good Hope quadrangle. The principal structural features brought out by the contours on No. 2 coal include two small domes. West of Roseville in T. 9 N., R. 3 W. (Ellison Twp.), is an incompletely defined dome on which the coal rises to an elevation of 736 feet, which is about 30 feet higher than to the south and east. The Parrish well in the northwest quarter of sec- tion 34 was drilled down on the flank of the dome where the coal is about 25 feet lower than at the apex. It failed to find any Hoing sand, and it might be said to discredit the area in the immediate vicinity so far as the presence of the sand is concerned. It does not discredit the structure, however, since the distribution of the sand is so erratic. A small dome lies just east of Roseville in sections 28, 29, 32, and 33. In section 28 the coal rises 20 feet higher than to the west, 30 feet higher than to the south, and 50 feet higher than to the east and north. A pronounced terrace extends to the south from the above men- tioned dome. It covers portions of sees. 9, 10, 15, 16, 19, 20, 21, 30, and 36, T. 8 N., R. 2 W. (Swan Twp.), where the coal lies at an ele- vation of about 680 feet, but rises to 693 feet in section 10. To the north and west the coal rises slightly, to the east it dips to an elevation of 620 feet, while to the south it slopes of! very gently. Six miles northwest of Bushnell there is a small dome in which the coal rises more than 20 feet above the adjacent region. Since it is in- completely defined, no recommendations can be accurately made ; how- ever,, a test in the southeast part of sec. 16, T. 7 N., R. 2 W. (Walnut the oil may occur in the troughs or synclines (fig. 14 C). This mode of Grove Twp.), can be suggested. 66 . OIL INVESTIGATIONS In the southwestern portion of the Goodhope quadrangle is a broad terrace upon which No. 2 coal lies at an elevation of about 680 feet. LOCALITIES ALREADY TESTED Five wells have been drilled within the borders of each of the two quadrangles in search of oil or gas. In the Goodhope quadrangle, the most favorably located well, so far as structue goes, was the Parrish well in sec. 34, T. 9 N., R. 3 W. (Ellison Twp.) This well failed to find the Hoing sand. Its relation to structure is discussed in the descrip- tion of the dome west of Roseville. A well drilled on the George Sailor farm in the NE. J4 sec. 21, T. 8 N., R. 1 W. (Greenbush Twp.), is located in a syncline and found no sand. A well drilled on the Matt Boden farm in the NW. % sec. 15, T. 7 N., R. 2 W. (Walnut Grove Twp.), is located upon the southern end of a gently sloping terrace. It likewise found no sand. Two wells were drilled on the Bruinga and Lester farms in sees. 7 and 18, T. 6 N., R. 2 W. (Macomb Twp.) The logs of these wells are somewhat indefinite, but it appears that the well in section 18 lies on a small dome. Four feet of sand was reported at the base of the second lime, with a small showing of oil. The well in section 7 found no sand. In the La Harpe quadrangle none of the five wells drilled is re- garded as being favorably located. No data are available concerning the well one and one-half miles southwest of Sciota, except that it was a dry hole. Of the four remaining wells, two, the Herzog in the NE. J4 sec. 30, T. 7 N., R. 4 W. (Blandinsville Twp.), and the Wilkes in the SW. ji sec. 25, T. 7 N., R. 5 W. (La Harpe Twp.), found no sand nor any show of oil. Of the other two the Gills in the NW. % sec. 8, T. 6 N., R. 5 W. (Fountain Green Twp.), is reported to have found 20 feet of sand with a showing of gas. This information has not been verified, and no log of the well is available. The Gochenour well in the NE.% sec. 3, T. 6 N., R. 5 W. (Fountain Green Twp.), found a showing of sand at the base of the second lime but no oil or gas. GAS IN THE GLACIAL DRIFT Small quantities of gas are frequently encountered in pockets of sand in the glacial drift. In a water well in the SW. J4 sec - 9, T. 8 N., R. 2 W. (Swan Twp.), gas rises in bubbles through the water in such quantities that when a pipe was inserted through the well platform, ~V^?V : .r..':-> ..V-,^" v 'V ; ,r ^ - ' Lk* -; ** '',,' ■> " :'xxV/- : --r^-^ '■■y^._y^^ r ''^'' r '^<.^ : i x' ■ D) ( structure sections in Central and Northern Pike County. .1 FIGURES 16. Diagrammatic illustration of conditions favorable to artesian wells. ... 85 17. Diagrammatic cross-section showing the upper coal bed (key horizon No. 7) and Colchester (No. 2) coal (key horizon No. 3) 90 TABLE 7. Summary of well data in central Pike County. 76 INTRODUCTION During the summer of 1918 a study of the structure of the north- ern and centra! parts of Pike County and the southeastern part of Adams County was made by the State Geological Survey in search of new areas favorable to the accumulation of oil. Figure 1 shows the area covered by this report. The Colmar oil field on the north and the Pike County gas field on the south suggest that the intermediate area, which has similar geolo- gical conditions, may prove productive. The area is partly covered by this report, together with the companion paper on Brown County, and the previous one for Schuyler County. 1 Favorable structures for testing are described in the following pages, as indicated* m the outline, and the uncertainties resulting from the irregular distribution of oil-bearing sands and other conditions are discussed. A brief description of the general geology of the region is also presented in the text and illustrations. 1 Morse, W. C, and Kay, Fred H., Area south of the Colmar oil field: 111. State Geol. Survey Bull. 31, 1915. PARTS OF PIKE AND ADAMS COUNTIES- 71 ACKNOWLEDGMENTS M. L. Nebel was in general supervision of the work for the early period, and introduced the writer to the geology of the region. Stuart Weller assisted in the identifications and correlations of the rocks. The reports of oil investigations in western Illinois by other members of the Survey were consulted in the study of the Hoing sand. Messrs. Jerry Mink, Earl Harris, and Claude Shinn kindly furnished the records of numerous wells drilled in central Pike County. PERSONNEL OF THE PARTY The party in immediate charge of the writer included M. C. Win- okur, as levelman throughout the season, and Marvin Weller for a short period near the close. Others employed as rodmen for variable periods were : Charles Aiken, George F. Baldwin, Milton Chestnut, Virgil Harte, George Holmes, Frank T. OrndorrT, Harry Ramsey, Otis Shake, George Stauffer, Virgil Tooley, H. E. Van Natta, and Fred Wright. TOPOGRAPHY OF THE AREA Plate IV is a map of the coal and gas fields in the northern and central parts of Pike County. This area lies upon the divide between the Mississippi and Illinois rivers. The western part is drained by Six Mile, Kiser, and Hadley creeks into the Mississippi, and the eastern part by Bay, Blue, and McGees creeks into the Illinois. The upland is hilly, except near Maysville and New Salem. The flood plains are narrow, and are dissected in many places by the winding stream channels. The soil and weathered rock on the slopes of the valleys, eroded into the shales of the Pennsylvanian ("Coal Measures"), creeps and slumps rap- idly and covers the consolidated rocks in the beds of the streams. For- tunately, the coal (Colchester) is exposed in numerous pits and banks that have been worked recently. Plate V is a map of southeastern Adams County. Only the area south of the "Base Line" was covered by the geological survey, but in order to show the location of the district in reference to the railroads, the map was extended two miles farther north to include Clayton, Camp Point, and Coatsburg. The belt of level upland which crosses the area near Beverly and Liberty forms the divide between the Mississippi and Illinois rivers. The southwest slope is drained by McCraney Creek into the Mississippi, and the northeast slope by McGees Creek and its tributaries into the Illi- nois. The upland north and northwest of Kellerville is a flat prairie 72 OIL INVESTIGATIONS lying on the divide between McGees Creek and Bear Creek drainage systems. There are very few exposures of the consolidated rocks in the level areas, and only a small number of farm wells pass through beds that can be identified from the available information. The study of the structure of the key beds is approximately limited to the stream val- leys where the contacts between the formations are exposed, and where numerous wells and pits pass through the coal bed. METHOD OF FIELD WORK The outcrops of the consolidated rocks were studied, and those that could be identified were located by pacing and compass, and described with considerable detail in reference to characteristic features represented on the postal road map which was used for a base. The map served later to guide the leveling party. The top of the Colchester (No. 2) coal was chosen as the principal key horizon for the entire area, except in the Pike County gas field, where the top of the gas rock was used as the datum plane (Plate IV). Contours and cross-sections show the ''lay" or structure of the key rocks. The structure, represented by contours on the coal, differs somewhat from the structure of the deeper beds at the horizon of the Hoing sand in the Colmar field, since the St. Louis, Salem, Warsaw, and Keokuk, which are present in the northern part of the area, are absent in the southern part (Plates VII and VIII). The lack of parallelism between the coal and the deeper beds is discussed on the later pages, but is not great enough to interfere seriously with conclusions drawn from study of the "coal contours". The intervals between the coal, as the principal key bed, and the other formations upon which points were located were measured wherever possible. The elevations of these points were re- duced or increased to the elevation of the top of the coal at each point by subtracting or adding the stratigraphic distance, as determined in the nearest measured section. The observed and the computed elevations of the top of the coal were plotted on the maps (Plates IV and V). Con- tours were drawn through points of equal elevations and show graphically the downfolds (synclines) and upfolds (anticlines) of the principal key bed, which appears as No. 3 in the following list of key horizons. KEY HORIZONS The following list gives the key horizons and the stratigraphic dis- tance to the top of the Colchester (or No. 2) coal. 7. Top of the upper coal bed, 75 to 80 feet above the Colchester coal. G. Bottom of second nodular limestone 63 to 72 feet above the Col- chester coal. 72 lying on t systems, the level a beds that ( of the struc leys where numerous The o that could I with consid on the pos later to gu The to key horizo: where the 1 Contours ai The structi from the si in the Coir which are southern pc the coal an great enou^ of the "coa key bed, ar measured \ duced or ir by subtract nearest mec the top of 1 tours were the downfo bed, which The fo tance to the 7. To coal. 6. Bo Chester coal PARTS OF PIKE AND ADAMS COUNTIES 73 5. Top of the Productus and Chonetes bed, 10 to 15 feet above the Colchester coal. 4. Top of septarian concretion layer, 6 to 8 feet above the Colches- ter coal. 3. Top of the Colchester coal (principal key horizon). 2. Top of the Salem limestone, 24 to 57 feet below the Colchester coal. 1. Top of the gas rock 293 to 298 feet below the Colchester coal and used as the key bed in the area within the stippled boundary (Plate IV). RELATION OF FOLDS TO ACCUMULATION OF OIL In most of the productive fields of Illinois oil occurs in the upper part of anticlines domes, and terraces. The localization of the oil ac- cumulations within these upfolds depends upon the extent of the sand body and the amount of salt water present. Where the oil sand extends over the anticline, and an abundance of salt water exists, the oil and gas occur in the positions shown in figure 14 A. With a less amount of salt water to buoy up the oil, the accumulation takes place farther down the slope of the anticline, localizing in the terraces (figure 14 B). If salt water is absent and the sand is not saturated with oil, the oil pools occur in the synclines (figure 14 C). In western Illinois the sand contains considerable quantities of salt water; the domes and terraces are discovered by geologic work, but the distribution of the sand can not be determined in advance of the drill. THE HOING SAND Oil was discovered in 1914 near Colmar on the farm of J. Hoing. The producing sand was described as the Hoing sand. Numerous wells were drilled in this locality, in some of which the sand is present and in others absent. The well records show that the Hoing sand is distributed in isolated lenses varying from a few feet up to 30 feet in thickness, and that it lies between the Maquoketa shale and the "second lime" of the drillers. The name has been mistakenly extended to include the produc- ing and non-producing sands in Schuyler County that lie immediately below the "second lime." The variability in thickness and distribution is probably due to the limitation of deposition of the sand to shallow disconnected depressions in the surface of the Maquoketa shale and to subsequent erosion. The shale beneath and the Niagaran limestone above prevent the migration of the oil and gas from one sand body to another. Each de- posit of sand is a unit within itself, in reference to the accumulation and 74 • OIL INVESTIGATIONS differentiation of the gas, oil, and salt water. A well on the crest of an anticline would test a lens of the sand if one were present, but it would not adequately test the entire fold. Wells drilled into lenses on terraces that lie below the crest of the anticline are known to be productive in the Colmar field, while the deposits of sand higher on the fold yield only salt water. 1 STRUCTURE OF THE AREA The beds have a general dip eastward which is interrupted by numerous undulations — synclines, anticlines, and terraces. Synclines In sec. 28, T. 3 S., R. 6 W. (Richfield Twp., Plate V), is a small basin in which the Colchester coal is 20 feet lower than in the adjacent area and has a thickness of 8 feet. Either this depression was probably a peat swamp for a longer time during the Carbondale epoch than the surrounding region, or the accumulation of the plant material was more rapid. The difference in elevation may be due in part to the difference in degree of compressibility of the thick plant deposit and the surrounding sediment. In the small syncline in the west half of sec. 8, T. 3 S., R. 6 W. (Richfield Twp., Plate V), the thickness of the coal was 3 feet. The Colchester coal was 11 feet thick in a small depression near the center of sec. 10, T. 4 S., R. 5.W. (Hadley Twp., Plate IV). Several years ago it was mined and used by the Wabash Railroal. Near the center of T. 3 S., R. 6 W. (Richfield Twp., Plate V), is a large syncline (Plate IX B-B) which would probably be found to ex- tend to the northeast corner of the township and then northwest to Lib- erty if the structure were completely defined. The flowing well on the farm of Luther Rice is located in the western part of the syncline, NW. Y A sec. 17, T. 3 S., R. 6 W., (Richfield Twp., Plate V). In the eastern half of T. 2 S., R. 5 W., (McKee Twp., Plate V), is a broad shallow syncline which has an area of approximately nine square miles. Anticlines and Terraces In sees. 3, 4, 5, 6, 9, 10, 11, 14, and 15, T. 3 S., R. 5 W. (Beverly Twp., Plate V), is an anticline which extends in a northeast-southwest direction. The north limb is slightly depressed in sections 11 and 4. A "nose" extends northward from section 5 and develops into a terrace 1 Morse, W. C, and Kay, Fred H., The Colmar oil field — a restudy : I'll. State Geol. Survey Bull. 31, p. 43, 1915. 74 different?" anticline not adec that lie the Co? salt w; num ba ar a s 4 PARTS OF PIKE AND ADAMS COUNTIES- 75 two miles wide, which lies in sees. 20, 21, 27, 28, and 29, T. 2 S., R. 5 W. (McKee Twp.) The coal in the terrace is 30 feet lower than on the crest of the anticline. The west and south slopes of the anticline are not completely defined ; but the information available shows that the coal dips at a low angle into the Richfield syncline on the west, and into the narrow basin near Beverly on the south. A narrow terrace lies in sees. 5, 6, 7, and 8, T. 2 S., R. 5 W. (Mc- Kee Twp.), and sees. 1, 2, 11, and 12, T. 2 S., R. 6 W. (Liberty Twp., Plate V). It is approximately four miles long and three-quarters of a mile wide. The fold becomes much broader toward the west, and may develop into a more favorable structure for oil accumulation under the drainage divide in Liberty Township. There are numerous small anticlines and terraces in T. 3 S., R. 6 W. (Richfield Township, Plate V), in which the Colchester coal rises only 10 feet or less above the coal bed in the nearby region. They are inter- esting for study but unimportant in relation to oil accumulations. North of Fish Hook, in sees. 5, 6, 7, and 8, T. 3 S., R. 4 W. (Fair- mount Twp., Plate IV), occurs a narrow terrace in a splendid location to serve as a collecting area for the long slope that extends for several miles into Brown County. It lies upon the eastern slope of the anticline in T. 3 S., R. 5.W. (Beverly Twp., Plate V). Two miles north of Hadley (Plate IV) is located an incompletely defined terrace which probably connects with the terrace in sec. 36, T. 3 S., R. 6 W. (Richfield Twp., Plate V). Pittsfield-Hadley Anticline 1 method of study From the owner of each gas well were secured the data given in the "Summary of well data of central Pike County", (Table 7), and from the drillers were obtained the well logs. The top of the gas rock was chosen as the datum horizon upon which to base the graphic repre- sentation of the structure of the region. The surface elevation of each well, as determined by the leveling party, was reduced to the elevation of the top of the gas rock by subtracting the interval from the surface to the gas-producing bed, as given in the log. Since there is an interval between the gas rock and the key bed (Colchester coal) used outside of the gas area of from 293 to 298 feet, the contours near the border of the gas area, which pass through elevations computed from the elevation of the coal, will not coincide vertically at the stippled boundary with the contours of the coal. This is noticeable in sees. 35 and 36, T. 4 S., R. 5 W. 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The axis extends from the SW. cor. of sec. 21, T. 4 S., R. 5 W. (Hadley Twp.), to the SE. cor. of sec. 22, T. 5 S., R. 4 W. (Pittsneld Twp.) The crest is divided into four separate dome-like structures by three saddles, one in sees. 1 and 2, T. 5 S., R. 5 W. (Derry Twp.), another in sees. 17 and 18, and a third in sees. 17 and 20, T. 5 S., R. 4 W. (Pittsneld Twp.). The structure section (Plate IX, C-C) shows three of the domes and two of the synclines that lie upon the anticline. The crest of the dome farth- est to the southeast is in the SE. J4 sec - 16 an d NE. ]/\ sec. 21, T. 5 S., R. 4 W. (Pittsneld Twp.). Two of the strongest gas wells in the area are located on this dome. The gas rock is 667 feet above sea level in the well in section 21 (No. 41 )\ Toward the north the gas-producing bed dips 220 feet to the mile, and to the south 100 feet to the mile. The eastward dip is 180 feet for the first mile and 40 feet for the second. In the wells in the city of Pittsneld, 3 miles from the top of the dome, the gas rock is 410 feet above sea level. One mile west of the crest of the dome the gas rock lies in the bottom of one of the saddles where its elevation is 596 feet. One-fourth mile farther west in sees. 17, 18, and 20, T. 5 S., R. 4 W. (Pittsneld Twp.), the gas rock has an elevation of 614 feet. The crest of this low dome lies in the SW. J4 section 17, the SE. *4 section 18, and the NW. Y\ section 20. The southwest dip is 70 feet in the first mile but decreases to 25 feet in the second, forming a terrace in section 25, T. 5 S., R. 5 W. (Derry Twp.), which is less than one-half mile wide. The only producing well in the southern half of Derry Township is located on this terrace. The gas sand in the syncline between the dome in sec. 17 and the one in sec. 7, T. 5 S., R. 4 W. (Pittsneld Twp.), is 555 feet above sea level. This is 55 feet lower than it is in either dome. From the crest of the dome in the center of section 7, the gas rock dips 70 feet in the first quarter of a mile, and 30 feet in the second, toward the north. The non-productive area is only a mile from the crest of the dome in this direction. On the south slope where the dip is 60 feet to the mile, the productive area is much broader. The dip of the gas rock from section 7, toward the northwest along the crest of the anticline, is 40 feet to the mile. In the center of sec. 2, T. 5 S., R. 5 W. (Derry Twp), the elevation is 557 feet above sea level. From the center of the NE. % sec. 2, T. 5 S., R. 5 W. (Derry Twp.), to the center of the south line of sec. 35, T. 4 S., R. 5 W., (Hadley Twp.), the gas sand 1 Well numbers refer to the reference numbers in Table 7. 82 OIL INVESTIGATIONS rises 31 feet, but the information is not sufficient to determine the struc- ture of the dome in detail. Two and one-fourth miles west of Summer Hill is an incompletely defined structure which is. probably a low dome. The gas sand in the productive well in sec. 10, T. 6 S., R. 5 W., (Atlas Twp.) is only 40 feet above the lowest known elevation of the sand in the syncline near New Hartford. DEVELOPMENT Gas was first discovered in Pike County in 1886, on the farm of Jacob Irick (F. G. Lewis, present owner), in sec. 1, T. 5 S., R. 5 W. (Derry Twp.), while drilling for water. The gas rock was entered at the depth of 186 feet. The well (No. 78) was cased and the gas was piped to the house, for which it has furnished an abundant supply since that time. Soon after the completion of the first well, a second one (No. 79) drilled for water on the same farm, "struck" gas at the depth of 168 feet. No further attempt was made to develop the field until 1905, when William Irick put down a well (No. 78) on his farm in the SW ^ sec. 1, T. 5 S., R. 5W. (Derry Twp.), and piped gas from it to the farm buildings for heat and light. During 1905 and 1906 two drillers, J. A. Clark and Jerry Mink, were constantly employed by the landowners who began to realize the advantage of the use of gas. Thirty wells were drilled in Derry and Pittsfield townships by June, 1906, six of them dry. Since then develop- ments have progressed much more slowly. Of the few wells drilled each summer, some furnished abundant supplies of gas. By the close of the summer of 1912, one hundred wells had been drilled, thirty-nine of which are now non-productive. The wells drilled since that time were oil tests, promoted either by a corporation or by a group of enterprising landowners. The initial pressure of the gas wells was not taken, but in almost every case the supply was more than was needed by the owner. It was noticed that the pressure was decreasing only when the demands exceeded the supply. In 1918 only those wells inclosed by the 590-foot contour (Plate IV) had sufficient gas supply for all seasons of the year. They are on the domes that lie on the anticlines. Between the 590- foot contour and the 500-foot contour the supply of gas is sufficient only for cooking and lights. A few wells near the 500-foot contour furnish enough gas for no more than one or two lights. The wells outside of the 500-foot contour are either non-productive or furnish such a meager supply of gas that they can be used only a few hours each day. On the southwest limb of the anticline in sec. 24, T. 5 S., R. 5 W. (Derry Twp.^ PARTS OF PIKE AND ADAMS COUNTIES- 83 is a well (No. 87) that was productive until 1917. It lies upon the anti- cline above the 520-foot contour. Two wells in sec. 13, T. 5 S., R. 5 W., (Derry Twp.) are non-productive and lie between the 530-foot and 540- foot contours. In sec. 35, T. 4 S., R. 5 W. (Hadley Twp.), the well (No. 9) shown on the top of the dome is non-productive because of de- fects in casing. The field has been thoroughly exploited. The produc- tive area is bounded on all sides by dry wells, and it is decreasing in size from year to year by failure of some of the wells that are near the margin. THE GAS ROCK The porous stratum forming the reservoir for the gas is a yellowish- brown dolomite, probably belonging to the Niagaran. Whenever the stratum was entered by the drill at an elevation above 500 feet, the well initially furnished an adequate supply of gas for farm use. This would indicate that the porous bed is present everywhere upon the anticline. The limestone above the gas rock, locally designated as the cap rock is only a few feet in thickness in most of the wells, and is overlain by the Kinderhook shale, which forms the impervious cover of the reservoir. The gas has very little odor and burns without smoke, giving a strong, bright flame. The following analysis is given by Professor T. E. Savage, who made an examination for the Geological Survey in 1906. 1 Per cent Carbon dioxide (C0 2 ) 81 Oxygen (0 2 ) 3.46 Marsh gas (CH 4 ) 73.81 Nitrogen (N) 21.92 Total 100.00 NOTES ON WELLS IN THE COLUMNAR SECTION SHEET ( PLATE VI ) The accompanying areal map of the crest of the Pittsfield-Hadley anticline gives the location of twenty-one wells which were chosen to show graphically the stratigraphic sequence of the region, the thickness of the formations and the variations in the elevation of the gas rock upon the fold. No. 58 is far down the slope of the southeast end of the anticline. The pressure was initially very weak, and the well is now abandoned. No. 47 furnishes gas for one light. No. 44 is one of the deepest wells in the area. It was drilled 18 feet into the gas rock. 1 Savage, T. E., Pike County Gas Field: 111. State Geol. Survey Bull. 1906. 84 OIL INVESTIGATIONS Nos. 41 and 27 are on top of the dome in section 16. They have furnished an abundance of gas since 1906. Nos. 60, 26, 31, 32, and 40 are on the slope of the dome in sections 16, 17, and 21, but are well up on the crest of the anticline. They supply the farms on which they are located with sufficient fuel for light and heat. No. 33 is a good well, located on a small dome in section 17. It was drilled during the spring of 1906. The pressure in No. 24 has noticeably decreased. The supply is not sufficient for heat during the winter months. It is located in the bottom of the saddle that crosses the anticline in sections 17 and 18. No. 17 is 76 feet deep. It is one of the shallowest and strongest wells in the area. It is located upon the top of the dome in section 7 and in the valley of a branch of Kiser Creek. Nos. 16, 19, and 86 are good producing wells, located on the slope of the dome in section 7. No. 75 is supplying gas for only one light. No. 81 has a good pressure of gas, but it is not being used. No. 9 was reported by Jerry Mink to contain considerable gas which was shut off by a strong flow of water. STRUCTURES FAVORABLE FOR TESTING The anticline in the northern half of T. 3 S., R. 5 W. (Beverly Twp., Plate V), is new territory for exploration for oil. Locations favor- able for tests of the structure are chosen with reference to the structural conditions only. The sand in Schuyler County has been shown to be in disconnected lenses, and that characteristic may be true for this area A well in the NE. y A sec. 5, T. 3 S., R. 5 W. (Beverly Twp.), would test the northwest end of the fold. The Hoing sand, which is the pro- ductive formation in the Colmar field, would be entered at the depth of 550 feet. To make the test complete, the drill should enter the Kimms- wick-Plattin limestone which lies approximately 700 feet below the sur- fac. The succession of strata that would be encountered is : Carbondale formation (shale), Pottsville formation (shale and sandstone), Salem limestone, Warsaw limestone, Keokuk limestone, Burlington limestone, Kinderhook group (shale), Upper Devonian shale, Niagaran limestone, Maquoketa shale, and Kimmswick-Plattin limestone. The southwest portion of the fold can be tested by drilling a well in sec. 10, T. 3 S., R. 5 W. (Beverly Twp.), preferably in the north half of the section. The depths to the Hoing sand horizon and the Kimmswick-Plattin limestone would be approximately as given in the above test. • f 1 t CO PARTS OF PIKE AND ADAMS COUNTIES 85 In T. 3 S., R. 4 W. (Fairmount Twp., Plate IV), is a narrow ter- race with a long northeast slope. Wells drilled near the northeast corner of section 8 would test the top of the structure. The Hoing sand horizon would be entered at the depth of 490 feet and the Kimms- wick-Plattin limestone at the depth of 680 feet. If it is found that the sand at the horizon of the Hoing sand in Schuyler ' and McDonough counties is in lenses, then other tests farther down the dip of the bed would be recommended. The dome in the center of sec. 7, T. 5 S., R. 4 W. (Pittsfield Twp., Plate IV), is probably the best location in the gas area. A well drilled in this area would pass through the following beds before the Kimmswick-Plattin limestone is reached: Upper Devonian shale, Niagaran limestone, and Maquoketa shale. The total depth of the test would be approximately 260 feet. The McSorley gas well (No. 17) enters the Hoing sand horizon at the depth of 76 feet. No sand was reported. Fig. 16. Diagrammatic illustration of conditions favorable to artesian wells. The dome in the SW. y A sec. 17, T. 5 S., R. 4 W. (Pittsfield Twp., Plate IV), would be tested by a well drilled in the south half of the quarter section. The succession of beds is the same as that above, with the addition of the Kinderhook shale, which lies upon the Upper Devonian shale. The test would enter the Kimmswick-Plattin lime- stone at the depth of 450 feet. The dome in the NE. y A sec. 21, T. 5 S., R. 4 W. (Pittsfield Twp.), has probably been tested by the deep well in the NW. Y\ of section 21, but since the gas rock is 30 feet lower in the test well than on the crest of the dome, which is one-half mile east, it is recommended that another well be drilled in the NE. J4 of section 21, in order to test the fold completely. The Kimmswick-Plattin lies approximately 400 feet below the surface. The terrace extending southwest from the anticline in section 21 can be tested by wells in the south half of sec. 19, T. 5 S., R. 4 W. (Pittsfield Twp.), and sec. 25, T. 5 S., R. 5 W. (Deny Twp.) The Kimmswick-Plattin limestone would be entered at the approximate depth of 420 feet. 86 ' OIL INVESTIGATIONS FLOWING WATER WELLS Flowing water wells depend on certain relations of rock structure, water supply, and elevation (fig. 16). A flowing well is possible in any place underlain by a bed of porous rock of considerable thickness beneath an impervious layer, if the porous bed outcrops over a rather wide stretch of territory in a region of higher elevation and adequate rainfall. The structure section (Plate IX, A-A) through the basin in which the Luther Rice flowing well is located, shows a part of these conditions. In this well the Niagaran limestone forms the porous water-bearing stratum beneath the impervious Kinderhook shale. The Niagaran beds outcrop near Mississippi River several miles to the southwest, and receive their supply of water from the rains in that region. STRATIGRAPHY General Statement The rocks of the area consist of unconsolidated and consolidated types. The unconsolidated are alluvium, loess, and drift ; the consoli- dated, shales, sandstones, coals, and limestones. Unconsolidated Rocks alluvium The alluvium occurs in stream valleys. It consists of glacial till, loess, and residual clay, reworked by running water. The sand con- stituent is high, and the amount of humus low. The thickness varies from a few feet to twenty or more. LOESS Covering the glacial drift in many places is a dust-like deposit known as loess. The similarity of its mineral composition to that of glacial drift may indicate that it is drift, reworked by water and wind. The history of its transformation into loess begins with transportation of drift material beyond the edge of the ice sheet by the streams flow- ing from the glacier, and its deposition upon the flood plains. After the retreat of the glacier the streams decreased in size, and the flood plains became dry, permitting the fine material to be picked up by the wind and deposited over the uplands. Its greatest thickness in this area varies from a few feet to 10 feet. DRIFT The heterogeneous deposit of clay, gravel, and boulders, which lies beneath the loess is known as drift and belongs to the Illinoian period 87 I to t is 1 it ock leet ing .ere in W. lay, •ille ■nts de- :ent 86 wa: an) ber wic rai] wh cor wa Nic sot reg dal loe sti frc kn- Th of in£ rel P h wi an be PARTS OF PIKE AND ADAMS COUNTIES 87 of glaciation. The thickness varies from a few feet on the upland to 30 or more feet in the valleys of the pre-Illinoian land surface. It is present everywhere in the area except where streams have removed it and have cut their valleys deep into the consolidated rocks. The rock fragments in the drift consist of many kinds picked up by the ice sheet from the various deposits over which it passed. In places extensive pockets of sand were deposited by the melting ice as in the SW. y A sec. 29, T. 5 S., R. 4 W. (Pittsfield Twp.), where a sand lens has a thickness of 28 feet. Lenses of gravel outcrop in many of the valley slopes, as in the NW. y A sec. 27, T. 1 S., R. 6 W. (Columbus Twp.) Masses of coal are found mingled with the clay, sand, and gravel of the drift, in sec. 29, T. 4 S., R. 3 W. (Griggsville Twp.). The predominance of shale particles and limestone fragments everywhere in the drift gives evidence that the major portion of the de- posit has been derived from the shales and limestones in the adjacent region. Consolidated Rocks generalized section Key bed numbers refer to the "list of Jcey horizons given on a previous page Thickness Pennsylvania]! system Feet inches Carbondale formation 37. Shales, light blue, sandy, in layers varying in thick- ness from % inch to 2 inches, and separated by thin seams of sand. The lower 6 to 8 inches con- sists of black shale 30 36. Coal, in lenses (key bed No. 7) 1 4 35. Shale; the upper 4 feet is bluish, streaked with ferrous oxide, and contains many stringers of coal. The lower 8 feet is blue, soft clay shale 12 34. Limestone, dark gray, nodular, crystalline (key bed No. 6) 3 6 33. Shale, light blue, micaceous, sandy, in thin beds.. 53 32. Limestone, bluish, shaly, fossiliferous. Productus and Chonetes shells are abundant (key bed No. 5) 3 31. Shale, light blue, sandy, containing many small nodules of limestone 4 30. Limestone, a band of large septarian concretions of dense bluish limestone, the crack filled with cal- cite crystals (key bed No. 4) 3 29. Shale, blue, sandy, with seams of pyrite 4 28. Shale, fissile, black 10 27. Coal, Colchester (No. 2) (key bed No. 3) 1 6 88 OIL INVESTIGATIONS Consolidated Rocks — Continued Thickness Feet inches Pottsville formation 26. Shale, bluish, sandy.. 24 25. Limestone, dolomitic, crystalline, brown 1 24. Shale, bluish, sandy, interbedded with thin beds of sandstone 5 Mississippian system St. Louis limestone 23. Limestone, bluish gray, brecciated, dense 3 22. Limestone, thin bedded, gray, crystalline 1 21. Shale, light green 20. Limestone, dolomitic, brown, crystalline 4 19. Shale, greenish 4 18. Limestone, brecciated, dense, bluish 6 17. Shale, green 16. Limestone, bluish gray, shaly, dense 8 15. Shale, light green Salem limestone 14. Limestone, fossiliferous, dove colored, containing numerous protozoans (top of formation is key bed No. 2) 10 13. Limestone, shaly 17 12. Limestone, brown, dolomitic 14 Warsaw formation 11. Shale, soft, interbedded with thin layers of fossilif- erous limestone. Bryozoans are abundant 28 10. Limestone, dolomitic, interbedded with shale 21 Keokuk limestone 9. Limestone, thinbedded, interbedded with layers of chert and shale, having a thickness varying from 1 to 4 inches. Limestone contains many frag- ments of crinoids and bryozoans. Brachiopods are abundant 24 Burlington limestone 8. Limestone, interbedded with thin layers of chert. The limestone contains abundant plates and seg- ments of crinoids 86 Kinderhook group 7. Shale, light blue, compact, with lenses of sand- stone and thin beds of limestone 122 Devonian system Upper Devonian shale 6. Shale, brown, calcareous 60 Silurian system Niagaran limestone 5. Limestone, dolomitic, gray, hard, dense ("cap rock" of the drillers) 14 4. Limestone, porous, dolomitic (gas rock, key hori- zon No. 1 ) 24 % % PARTS OF PIKE AND ADAMS COUNTIES 89 Consolidated Rocks — Concluded Ordovician Thickness Maquoketa shale Feet inches 3. Shale, greenish blue, with limestone beds near the base 166 Kimmswick-Plattin limestone 2. Limestone, dolomitic, white and gray 295 St. Peter sandstone 1. Sandstone, hard, gray, and brown (Total thickness in the area is unknown. Well No. 113 enters the formation to the depth of 95 feet 6 inches) PENNSYLVANIAN SYSTEM CARBONDALE FORMATION The Carbondale formation includes all the beds lying between the top of No. 6 coal and the base of No. 2 coal. Only the lower part of the formation occurs in this area. The upper beds were not deposited or were removed during the period of erosion that followed the depo- sition of the Pennsylvanian rocks in western Illinois, and preceded the advance of the Illinoian ice sheet. The greatest thickness of the Car- bondale formation is in the northern part of the area in Adams County (Plate VIII). In the wells near Clayton, it has a thickness of 150 feet. In T. 3 S., R. 6 W. (Richfield Twp.), it has the average thick- ness of 115 feet. On the north limb of the Pittsfield-Hadley anticline (Plate IV) four miles south of Baylis, the total thickness of the Car- bondale is only five feet. The highest beds of the formation in this area are exposed in the stream valleys near Columbus and Camp Point, and on the highest hills in T. 3 S., R. 5 and 6 W., (Beverly and Richfield townships, Plate VIII), for example in the SW. % sec. 27 of Richfield Township. They consist of light blue, sandy shales in layers varying in thickness from one-half inch to two inches, and are separated by thin seams of sand. Thirty feet is the greatest thickness exposed in a single section. Beneath this shale and seventy-five feet above the base of the Car- bondale formation is a bed of coal consisting of numerous small lenses varying in thickness from a few inches to several feet (figure 17) and overlain by 6 to 8 inches of black shale similar to that above Colchester (No. 2) coal. The underclay is bluish, streaked with yellow, and con- tains many thin seams of coal. Lenses of the coal bed in sees. 10, 14, 22, 24, and 25, T. 3 S., R. 6 W., have been mined by stripping. The coal stratum has been traced only in T. 3 S., R. 6 W. (Richfield Twp.) Below this lies a 12-foot bed of soft, blue, calcareous shale. Near the base many small nodular masses of limestone occur. 90 OIL INVESTIGATIONS The bed of limestone beneath the shale is a brown nodular forma- tion showing an average thickness of three feet, and carrying a high percentage of clay. The best exposures are in sees. 14, 22, and 24, T. 2 S., R. 6 W. (Liberty Twp., Plate VIII), and sees. 19 and 31, T. 2 S., R. 5 W. (McKee Twp., Plate VIII). Near the center of sec. 31, T. 2 S., R. 5 W. (McKee Twp., Plate VIII), is a splendid outcrop of the thick deposit of shale which underlies the nodular limestone. It is a light-blue, micaceous, sandy shale, in lay- ers varying from a fraction of an inch to 4 or more inches, which are separated by sandy seams. The formation weathers rapidly, and talus debris covers the bases of all the bluffs in which it is exposed. The maximum thickness measured is 53 feet. Fig. 17. Diagrammatic cross section showing the upper coal bed (key horizon No. 7) in lenses at 725 feet and Colchester (No. 2) coal (key horizon No. 3) just below 650 feet above sea level. The location of this sec- tion is shown as E-E on Plate VIII. A very persistent, impure, fossiliferous limestone lies beneath the thick shale deposit and 10 to 15 feet above the Colchester coal. The fossils are principally Productidae shells. It has a thickness of 3 inches in the section along the stream in the west half of sec. 8, T. 3 S., R. 6 W. (Richfield Twp., Plate VIII). Four feet of light-blue, sandy shale lies between the fossiliferous bed and the horizon of the septarian concretions. The shale contains many small concretion-like nodules, arranged parallel to the stratification. The septarian concretions resemble crushed spheres of dark-blue limestone, with the cracks formed by the stress filled with crystals of calcite. They lie in a band 6 to 8 feet above the top of the Colchester coal. The next 7 feet of shale below the concretions is a dark-blue, car- bonaceous deposit, containing many seams of pyrite. Between the bed of shale above and the Colchester coal beneath is a bed of black fissile shale with an average thickness of 10 inches. PARTS OF PIKE AND ADAMS COUNTIES 91 The Colchester coal and the black shale immediately above are in a few places the only representatives of the Carbondale formation, as in sec. 22, T. 5 S., R. 4 W. (Pittsfield Twp., Plate VII). In most of the pits, banks, tunnels, and exposures in the bluffs of the streams, the thickness of the coal varies from 18 to 24 inches. In sec: 28, T. 3 S., R. 6 W. (Richfield Twp., Plate VIII), and sec. 10, T. 4 S., R. 5 W. (Hadley Twp., Plate VII), the coal has a thickness varying from 8 to 11 feet. POTTSVILLE FORMATION The Pottsville formation underlies the Colchester (No. 2) coal conformably. Its thickness varies from 30 to 40 feet in T. 1 S., Rs. 5 and 6 W. (Concord and Columbus Twps., Plate VIII), to a few feet in T. 5 S., R. 4 W. (Pittsfield Twp., Plate VII). The following is a section measured on the bluff of a stream, in the SE. cor. NW. y^ sec. 5, T. 3 S., R. 4 W. (Fairmount Twp., Plate VII). Section of strata northwest of CTiestline Feet Inches Carbondale 3. Colchester coal 1 6 Pottsville 2. Shale, yellowish, sandy 4 1. Shale, bluish green, sandy , 10 Base not exposed. A section measured in the NW. cor. SE. }i NE. y A sec. 33, T. 2 S., R. 5 W. (McKee Twp., Plate VII), is as follows: Section of strata northeast of Fair Weather Feet Inches Carbondale 4. Colchester coal 1 2 Pottsville 3. Shale, bluish 24 2. Limestone, brown 1 3 1. Shale, bluish, sandy 5 6 Salem limestone. Base not exposed. The variation in thickness is probably due to the irregularities of the surface upon which the Pottsville was deposited. The rocks of the Pennsylvanian system lie immediately beneath the drift over 78 square miles in the central and northwestern part of the area in Pike County, and over almost all the area in Adams County repre- sented by Plate VIII, except along the southwest border and in the val- leys of the larger streams. Outliers of the Pennsylvanian sediments lie upon the limbs of the anticline in the gas area, between Pittsfield and Hadley (Plate VII). 92 OIL INVESTIGATIONS MISSISSIPPIAN-PENNSYLVANIAN UNCONFORMITY After the deposition of the St. Louis limestone, western Illinois was drained of its sea and remained land until the invasion of the Ste. Genevieve sea, which extended up the Mississippi valley into Iowa. The invasions of the Chester sea did not extend so far north, and probably did not cover Pike and Adams counties in Illinois. During the long period that intervened between the retreat of the Ste. Genevieve sea and the deposition of the Pottsville sediments, the area described in this paper was above the sea and subjected to the agencies of erosion. The St. Genevieve formation was eroded completely from the area, and the St. Louis and Salem formations were removed from much of the area south of their present boundaries (Plates VII and VIII). MISSISSIPPIAN SYSTEM The Chester group and the Ste. Genevieve limestone are absent. The rocks of the Meramec, Osage, and the Kinderhook groups outcrop in the area. The Meramec. group includes the Salem and St. Louis lime- stones. The Osage group includes the Warsaw formation, the Keokuk limestone, and the Burlington limestone. No attempt was made to dif- ferentiate the members of the Kinderhook group. ST. LOUIS LIMESTONE The St. Louis limestone is the surface formation over approxi- mately 16 square miles in the valleys of McGees, McCraney, and Mill creeks (Plate VIII). Along McGees Creek the formation disappears near Hazelwood, and the overlying Pennsylvanian shale is in contact with the Salem limestone (Plate IX, B-B). In the valley of McCraney Creek the St. Louis extends much farther south. The best exposures of the formation are along this creek in sees. 4, 9, and 17, T. 3 S., R. 6 W. (Richfield Twp., Plate VIII). The St. Louis is essentially a brecciated, bluish-gray limestone, very brittle and compact. The angular fragments vary in size from minute particles to masses several feet in diameter. Be- tween the strata of limestone are seams and beds of greenish clay. The formation has an average thickness of 20 feet along McCraney Creek. The thickness increases down the dip, and from the well of Russel Davis in sec. 25, T. 1 N., R. 5 W. (Clayton Twp.), 150 feet of St. Louis is reported. Fossils are very rare in the limestone layers except locally, where numerous masses of Lithostrotion occur. Many of these fossils were weathered out of the limestone before the deposition of the Potts- ville and have become imbedded in the base of that formation as in sec. 5, T. 2 S., R. 5 W. (McKee Twp., Plate VIII). The following is a section of the St. Louis measured from a bluff near the stream in the NW. cor. sec. 5, T. 2 S., R. 5 W. PARTS OF PIKE AND ADAMS COUNTIES 93 Section of strata northwest of Hazelwood Feet Inches Recent 11. Soil 2 St. Louis 10. Limestone, bluish gray, brecciated, dense 3 9. Limestone, thin bedded, gray, crystalline 1 6 8. Shale, light, green . . 6 7. Limestone, dolomitic, brown, crystalline 4 6 6. Shale, greenish 4 5. Limestone, bluish, brecciated, dense 6 4. Shale, green . . % 3. Limestone, bluish gray, shaly, dense 8 2. Shale, light green . . Y 2 Salem 1. Limestone, dolomitic, massive, brown crystalline. Base covered 5 SALEM LIMESTONE The Salem limestone lies unconformably below the St. Louis lime- stone. It outcrops in the valleys of McCraney and McGees creeks, and in the eastern part of T. 3 S., R. 4 W. (Fairmount Twp., Plate VII). It overlaps the Warsaw and Keokuk and in central Pike County (Plate VII) lies upon the Burlington limestone. The lower beds of the Salem formation, which are present in Brown and northern Pike counties, are absent in the southern part of T. 3 S., R. 4 W. (Fairmount Twp). Cen- tral Pike County was probably land during the early Salem time. Fossils are locally abundant, consisting of numerous shells of proto- zoans and fragments of bryozoans. The formation has a thickness of 41 feet along McGees Creek and decreases southward, completely disappearing in the northeast part of T. 4 S., R. 4 W. (New Salem Twp., Plate VII), where the Pennsylvanian shales lie upon the Burlington limestone. WARSAW-SALEM UNCONFORMITY After the deposition of the Warsaw, there was a prolonged period of erosion during which the Warsaw and Keokuk beds were probably eroded from much of the Pike County area (Plate VII), leaving the Burlington limestone as a surface formation at the beginning of the Salem time (Plate IX, D-D). This unconformity is the basis for the division of the Mississippian limestones in this area into the Osage and Meramec groups. WARSAW FORMATION The upper part of the Warsaw formation consists predominantly of soft, calcareous shale, interbedded with thin crystalline limestone 94 OIL INVESTIGATIONS strata. The limestones are very fossiliferous, containing many shells of brachiopods and remains of bryozoan colonies. Lioclema and Arch- imedes are abundant. The lower part of the Warsaw formation con- sists of a series of dolomitic limestone, interbedded with shales. The limestones are compact, light gray, and contain only a few fossil re- mains, which are mostly fragments of bryozoans. This formation outcrops along McCraney and McGees creeks (Plates VII and VIII). The contact between the Warsaw and Keokuk is not sharply defined, and the faunal characteristics of the two forma- tions are very similar. There appears to be no cessation in deposition and no distinct break in the succession of the life of the two formations to suggest an unconformity. In a section measured along McGees Creek, in sec. 4, T. 3 S., R. 4 W. (Fairmount Twp., Plate VII), the Warsaw has a thickness of 49 feet. KEOKUK LIMESTONE The Keokuk limestone is exposed along McGees (Plate VII) and McCraney creeks (Plate VIII). It consists of fossiliferous lime- stones and shales interbedded with layers of cherty limestone. The shaly layers are filled with fragments of bryozoans. Brachiopods and crinoids are abundant in the limestone beds. Echinoconchus altematus, Productus magnus, Agaricocrinus tuberosus, and several genera of Spirifera were collected from the exposure of the limestone in the NW. 34 sec. 4, T. 3 S., R. 4 W. (Fairmount Twp.) The Keokuk has a thickness of 24 feet in this locality. BURLINGTON LIMESTONE Burlington limestone is the surface formation near the southern boundary of the area in Adams County. (Plate VIII) and over a con- siderable portion of the eastern, southern, and western parts of the area in Pike County (Plate VII). It varies in thickness from 6 feet on the crest of the Pittsfield-Hadley anticline to 100 feet in the Sam Brad- shaw well, NW. cor. NE. ]/ A sec. 4, T. 4 S., R. 3 W. (Griggsville Twp., Plate VII). The formation consists of alternating beds of limestones and cherts. The limestones are conspicuously crinoidal, consisting almost entirely of separated plates and column segments. Productus burlingtonensis is present in considerable abundance. The cherty beds make up approx- imately fifty per cent of the formation. In many of the wells upon the anticline in the gas area of Pike County, the Burlington limestone is represented only by cherty layers. PARTS OF PIKE AND ADAMS COUNTIES. 95 KINDERHOOK GROUP Shales and thinly bedded sandstones of the Kinderhook group out- crop upon the anticline in central Pike County (Plate VII). The thick- JL , [ bnxj . ' ^^xxv. waooLj uj ucus ui wnite and gray limestone. The formation has a thickness of 295 feet in the well (No. 113) drilled by the Summer Hill Light and Fuel Company. In the outcrops in Calhoun County the formation is composed largely of shells. A show of oil is reported from these beds in many parts of Illinois. 94 OIL INVESTIGATIONS strata. The limestones are very fossiliferous, containing many shells of brachiopods and remains of bryozoan colonies. Lioclema and Arch- 1 ^ 1 " -■ 1 — ~ + ~-P fl-»f» "\A/"orcQAAr -formation con- The limestones arc Lunspimuuoij wm ~^—., ___ of separated plates and column segments. Pro ductus burlingtonensis is present in considerable abundance. The cherty beds make up approx- imately fifty per cent of the formation. In many of the wells upon the anticline in the gas area of Pike County, the Burlington limestone is represented only by cherty layers. PARTS OF PIKE AND ADAMS COUNTIES- 95 KINDERHOOK GROUP Shales and thinly bedded sandstones of the Kinderhook group out- crop upon the anticline in central Pike County (Plate VII). The thick- ness varies from a few feet to a maximum of 122 feet, observed in the well of Claude Shinn in the SE. cor. sec. 36, T. 5 S., R. 5 W. (Derry Twp., Plate VII). The formation is probably absent over the central portion of section 7 (Plate IX, C-C, well No. 17, and Plate VI). DEVONIAN SYSTEM UPPER DEVONIAN SHALE Between the Kinderhook shale and the "second lime" occurs 60 feet of dark-brown, calcareous shale, which is referred to as the Upper De- vonian, and known in this area only from well records. Upon the basis of the interpretation of the log of the gas well (No. 17, Plate VI), one-fourth of a mile west of the center of sec. 7, T. 5 S., R. 4 W. (Pittsfield Twp.), it is the surface formation over a small area in the valley of Kiser Creek. No attempt has been made to define the limits of the outcrop on the map of the areal geology. (See Plate IX, C-C.) SILURIAN SYSTEM NIAGARAN LIMESTONE Niagaran limestone lies below the brown shale. Only a few of the wells pass through the formation into the Maquoketa shale beneath. The upper part of the formation is a white, hard, compact, dolomitic limestone, locally called the "cap rock ;" the lower portion is a brown dolomite and contains the gas in Pike County. The thickness, as de- termined from the oil test in sec. 36, T. 5 S., R. 5 W. (Derry Twp.), is 38 feet. The Hoing sand, probably derived from reworked material, is locally deposited upon the irregular surface of the Maquoketa for- mation, and forms the base of the Niagaran. ORDOVICIAN SYSTEM MAQUOKETA SHALE In the well (No. 113), drilled by the Summer Hill Light and Fuel Company in sec. 12, T. 6 S., R. 5 W. (Atlas Twp.), 166 feet of green- ish shale was encountered below the Niagaran limestone. This shale has been correlated with the Maquoketa shale of northern Illinois. KIMMSWICK-PLATTIN LIMESTONE The Kimmswick-Plattin limestone consists of beds of white and gray limestone. The formation has a thickness of 295 feet in the well (No. 113) drilled by the Summer Hill Light and Fuel Company. In the outcrops in Calhoun County the formation is composed largely of shells. A show of oil is reported from these beds in many parts of Illinois. EXPERIMENTS IN WATER CONTROL IN THE FLAT ROCK POOL, GRAWFORD COUNTY By Fred B. Tough, Samuel H. Williston and T. E. Savage In cooperation with the U. S. Bureau of Mines OUTLINE PAGE Introduction 99 Summary 99 Purpose of the work 99 Results of corrective work 101 Permanency of results 101 Decline curves 101 Acknowledgments 104 Statement of problem 104 Selection of Flat Rock pool for experimental work 106 Geology 106 General statement 106 Geologic section 107 Quaternary system 107 Pennsylvanian system 107 Pottsville formation 110 Carbondale formation 110 McLeansboro formation 110 Producing sands Ill The 600-foot gas sand Ill Structure Ill Upper salt sand Ill Flat Rock sand 112 Structure 113 Oil characteristics 114 Water characteristics 114 Investigation prior to recommendation 118 Peg model 118 Graphic logs 121 Preliminary gaging 121 Method of recording data 124 Ratio 128 Recommendations for repair work on wells 128 Gaging after repairs 129 Loss of production incident to delay in repairs on wells 129 Testing to determine source of incoming water 131 Use of Venetian red as an indicator 131 Use of packers as testing devices 131 (97) 98 OIL INVESTIGATIONS Outline — Continued PAGE Methods of water control 131 Use of mud fluid 131 The mud 133 Methods of mudding wells 134 Suggestions with regard to casing 136 Application to repair problems 137 Corrosion of casing and methods of prevention 137 Intermediate water and its control 138 Use of cement 139 McDonald method of cementing bottom water 140 ILLUSTRATIONS PLATE PAGE X. Map showing structure on the surface of the 600 foot "gas sand" in a portion of the Flat Rock pool 110 XI. Map showing structure on the surface of the Flat Rock sand in a portion of the Flat Rock pool 114 XII. Map showing water and oil production and the water-oil ratio of wells in a portion of the Flat Rock Pool; the map also shows leases 128 FIGURE 18. Diagram showing rise and decline of oil production in Illinois, 1905-1918 100 19. A. Diagram showing the production of oil and water for Ewing well No. 8, Selby-Cisler Producing Company, beginning immed- iately alter cementing B. Diagram showing the production of oil and water for Ewing well No. 8, same company, beginning immediately after packer was set 102 20. Photograph of a casing corroded by water in the Flat rock pool 105 21. Map showing contours on Beaume oil gravities. The lighter oils are in the higher parts of the structure. (Compare Plates X and XL) 115 22. Photograph of the peg model, used in the field to represent sub-sur- face conditions 119 23. A graphic log typical of those used in studying wells with sub- normal production 120 24. Photograph of a single-barrel gage setup used early in the work.. 123 25. Diagram showing in detail the plan of the single-barrel gage in a setup 123 26. Photograph of the three-barrel siphon gage setup in operation. . 124 27. Diagram showing in detail the plan of the three-barrel siphon gage setup. The apparatus is shown on the tank rather than beside it as in the photograph (figure 26) of a similar setup 125 28. Sample record sheet as used in gaging 126 29. Lease sheet showing gage averages 126 30. Photograph of the gage board devised for protection of the records while in use on the lease 127 WATER CONTROL, FLAT ROCK POOL 99 Illustrations — Concluded PAGE 31. Diagram to show the saving in casing accomplished by the use of mud fluid 132 32. Photograph showing the connection at the top of the well between the discharge of the mud pump and the casing in the circula- tion method. The outcoming mud fluid has been forced down through the casing, out its bottom, and is returning to the surface, outside the casing 133 33. Diagram showing the system used in collecting mud for mudding Selby-Cisler well, Ewing No. 6B 135 34. Photograph of the mud sump taken from the top of the derrick on Selby-Cisler well, Ewing No. 6B 137 35. Photograph of the mud sump looking toward the derrick. Trench near the center in which coarse material settles out; suction and mixing pipes at the right the former below the latter.. 139 TABLES 8. Results of corrective work 103 9. Analyses of water from oil wells in the Flat Rock Pool 116 10. Summary of recommendations for repairs to wells 130 INTRODUCTION The phenomenal development of petroleum in the State of Illinois between the years 1905 and 1910 and the subsequent decline is strik- ingly shown in the curves of figure 18. It is this alarming decline in the amount of crude oil produced yearly that constitutes the most ser- ious problem confronting the oil industry of the commonwealth. Be- sides the total production of the State, the curves included in figure 18 show the relative productivity of the various pools. It will be noted that the total State production for the year 1917 was nearly 4,000,000 barrels less than the amount extracted from the Lawrence County pool alone in the year 1911, and. about 3,000,000 barrels less than the yield from the Crawford County pool in 1908. SUMMARY Purpose of the Work The fundamental purpose of the present work is to combat this enormous decline of oil production in Illinois. Pursuant to this end it was determined to make an intensive study of a small area in one of the oil fields of the State, with the hope that the results attained might encourage an extension of similar work throughout the State. The methods of gaging wells and of applying data to the various problems encountered are given in considerable detail, as it is thought that such information might be of use to operators conducting a study of similar problems. It is also hoped that the State and Federal governments will 100 OIL INVESTIGATIONS 35 — 30 / / / 25 / / 20 C 5 2 o £ 3 3 -J 5 / / 15 / 10 / \\ / L ) 5 \ J i I 7/ // / /// (/ 1 > / / A / / — i r » — — ( >■ — "^ V =4 &eee =3 1= ^ r 06 I9f0 12 14 16 17 Fig. 18. Diagram showing rise and decline of oil production in Illinois, 1905- 1918, expressed in barrels of 42 gallons. A. Total for State. D. Clark Co. Pool. G. Plymouth Pool. B. Crawford Co. Pool. E. Sandoval Pool. C. Lawrence Co. Pool. F. Carlyle Pool. be able to furnish necessary assistance and advice to operators in solv- ing their oil-field problems. WATER CONTROL, FLAT ROCK POOL 101 Results of Corrective Work The corrective work discussed in this bulletin and summarized in Table 8, is entirely a commercial enterprise, and its practical value therefore depends upon the calculable profits resulting from it. The total increase in "settled" production for the ten wells upon which repair work was done amounted to 66.5 barrels a day, at a repair cost of $3,975. In other words this "settled" production was obtained at a cost of $59.77 per barrel. The average increase of oil production per well was six barrels a day at the end of six months, and the average water decrease was TOO barrels a day. The average cost of repairs was $361 per well. Not taking into consideration the saving shown by the decreased water production, but only the additional profit represented by the six- barrel increase, the cost of repair work was repaid in less than a month's time. It will be noted that repair work on one well only (Ohio No. 5) resulted in a loss of oil. Even here, however, the decrease of water is so enormous as to partially compensate for the loss in oil, and all or part of this loss may perhaps be regained by cleaning out the cement and using a smaller quantity for the next attempt. From Ohio No. 10 there was no increase in oil, although the water was cut down considerably. From these two wells only no production gains were made. All other wells showed increased amounts of oil and decreased amounts of water lifted. From each of six wells the oil production was increased on the average more than six barrels a day. Two of them increased in pro- duction ten barrels or more per day, and one increased twenty barrels. From five wells were eliminated more than 100 barrels of water a day, and from one over 300 barrels were shut ofT by the use of cement. Permanency of Results decline curves The immediate question concerning cementation and other similar repairs is as to their effective length of life. In reference to the proba- ble length of life of the increase, frequent gages were taken on cor- rected wells. Two of the resultant curves on different types of repair work are shown in figure 19. In an effort to control lower water, well No. 8 (fig. 19, A) was cemented with some difficulty in the early part of July. The work was not entirely satisfactory, but production was increased so that it was deemed unwise to try to correct it at the time. When the repair work- was completed the production was oil, 65 barrels and water, 125 barrels, which amounted to an increase of 550 per cent of oil and a decrease of 102 OIL INVESTIGATIONS / i L ° v v s -o- 2 JULY ' AUGUST ' SEPTEMBER ^ -A > i 1 1 / >"-N V / V JAJJ ,tt_ / > ^ / Fig. 19. A. Diagram showing the production of oil and water for Ewing well No. 8, Selby-Cisler Producing Company, beginning immediately after cementing. The production before cementing was: Oil, 10 barrels and water, 220 barrels. B. Diagram showing the production of oil and water for Ewing well No. 5, beginning immediately after the packer was set. -The production before packing was: Oil, 1.6 barrels and water 70.0 barrels. WATER CONTROL, FLAT ROCK POOL 103 PI h o 2 co o pi d o O u u So 4-1 O CO i-i cd a PI s >> cd bjo a u ,q cu be >,cd cu ft bi P o ,p o pi 'St B « PI s Pi CJ B 4-J o Ofl 3^ C o o CJ-rH fc Eh O Ph ^ Pi CJ •id • m m co co e* m co o CO m o CJ CO £o> s> ■* • d c» d ed ■* ■<* o CD d t< m CO c t- CM CO co »n s> i-> CM o o pi 1-1 1 Ol ^ ■d o i-i (-1 cj ^j in . ! -* « m t- a •od cm in . co \d d CM eo" !h 5> 5> 3> o o CO w tM £ 0) !-i CO o lO CM CO -*< t- c m co CM ^ CM (M $ (M in j^ a D QQ*s 1 - «« 1 ee 1 CO to h CJ >-. ■s CO Za 'i S-i I ft I "JOT in m . \ *~. in m m CO co oo m JO ■P o co 1 d CM o 1 m r jco d to o co T d d co 1 m CM s M ^" o ^^ IS n cd so— ' •2 ACQ m . : : bu • 10 CO . Pi : u ^cm' CO" d CO ho CO bo "S CO >> d 6 ^ d CO o m CO CO o _; CO o Sd Pi o CO A 1 ~ co — £ <-> ft •id +.1 pi £^ in 6 d in d d O !h ft oqco CO CO 1-1 H CU •d • CM o cd i-J •© : in d CM , 4> 0) S-i 8- CO in d ° d in CO ® CM CM CO Us c ^ P ■pj cu « s 73 3S co CO 0) CO co CJ CO CO CJ CO co CO co ^ pi o B CU fl co-c 3) PI cd CO 5 to O to 6 CO 6 1 -3 2 '3 CJ P ip CJ p td cu a S o O C c d pi cd t3 PI cO c cd -d pi CO | cd P3 P3 _c o P JQ _c 5 5 c P p £ 3 a3 0) ^ 73 CJ CJ CJ CJ CJ C c ) CO l/l c w If) 1 C/] D O O 104 OIL INVESTIGATIONS 43 per cent of water. Twelve days later the oil had dropped to 35 barrels and water increased to 210 barrels. Both oil and water then declined slowly during the ensuing two months. The final gage showed 30 barrels of oil and 184 barrels of water. In figure 19 B, is shown a decline curve for a well on which the problem was one of upper water elimination. In contrast with the cement curve, the water decreases sharply and then rises slowly. The oil rises rapidly at first as the water is eliminated, and then more slowly. It will reach its maximum and then start on the natural decline curve of the pool. After the first acute adjustment is made the changes are quite gradual, in both the upper water and lower water problems, and if the work is done carefully the beneficial effects should last some length of time. ACKNOWLEDGMENTS The work was started by Mr. Merle L. Nebel and had been carried almost to completion at the time of his death in October, 1918. Acknowledgments are due the Ohio Oil Company, the Central Refin- ing Company, the Selby and Cisler Refining Company, James Pease and Company, and the Indian Refining Company for their hearty cooperation in supplying necessary data, their assistance in the preliminary field study, and their response to recommendations for corrective work. Special acknowledgments are made to the Ohio Oil Company for necessary material used in the work, to the Illinois Pipe Line Company for the special equipment they supplied, and to the oil men of the dis- trict for their interest. Acknowledgments are also due the Illinois State Water Survey for helpful cooperation and for numerous analyses. Mr. Frank J. Madden assisted in the gaging of wells and other work in the field. Great aid was given by the numerous farm and lease foremen, employees, and officers of the companies, especially Mr. J. K. Kerr, Mr. C. W. Baker and Mr. Walter Lowrie, Mr. John Bell, Mr. R. S. Blatch- ley, Mr. Carl Morrison, Mr. Lawrence Myers, Mr. W. J. Hurd, and Mr. Charles Karnes. The work was a cooperative one, and grateful ac- knowledgment of the assistance they rendered is made. STATEMENT OF PROBLEM One of the most widespread and troublesome problems affecting production throughout the State is the great amount of water being WATER CONTROL, FLAT ROCK POOL 105 pumped to the surface along with the oil in the process of recovery. The water is separated from the oil by gravity. The methods of pumping and preparing oil for the market have been covered by Blatchley. 1 It is usually necessary to steam the oil before the water will settle out sufficiently to render the product acceptable to the pipe-line companies. Fig. 20. Photograph of a casing corroded by water in the Flat Rock Pool. Pumping large amounts of water with the oil is subject to the follow- ing economical disadvantages : 1. Power is wasted in lifting the water to the surface. While it can not be said that the power cost would vary in direct proportion to the amount of fluid handled, nevertheless if the water content were eliminated it is certain the cost of production would be materially decreased. 1 Blatchley, Raymond S., The oil fields of Crawford and Lawrence counties: 111. State Geol. Survey Bull. 22, p. 159, 1913. 106 OIL INVESTIGATIONS 2. Corrosion of casing (fig. 20), rods, and lease piping occasions considerable expense of replacing such equipment which could be avoided if the amount of water were reduced. 3. The production of a well is often greatly reduced by ingress of water. The exclusion of water from oil and gas productive strata was therefore undertaken as the first step in retarding the decline of oil production. This phase of the subject is dealt with exclusively in the present report. SELECTION OF FLAT ROCK POOL FOR EXPERIMENTAL WORK Several reasons combined to determine the selection of the Flat Rock pool. It presents a comparatively well-defined area and can therefore be considered as a unit free from the more complicated factors that might have developed in considering a like area of one of the larger pools. Also much trouble has been occasioned in this pool by the infiltration of highly corrosive waters, both top and bottom, into the wells. In fact, the water troubles in this pool are found so pro- nounced that any demonstration work accomplished in it should be highly convincing as to its effectiveness. A portion of the Flat Rock pool embracing approximately 300 acres, in sec. 31, Honey Creek Town- ship (T. 6 N., R. 11 W.), was selected for intensive study. As shown on the map, Plate XII, the properties involved were under lease to four companies, as follows : Central Refining Company — 12 producing wells. James Pease Company — 9 producing wells. Ohio Oil Company — 13 producing wells. Selby and Cisler Producing Company — 15 producing wells. GEOLOGY 1 General Statement The Flat Rock oil pool lies adjacent to the town of Flat Rock, in the southeast part of Crawford County, ten miles southeast of Robin- son, the county seat. From Flat Rock it extends towards the northeast for a distance of five and one-half miles, including the small production in new territory at the northeast end. The area comprises all, or parts, of sections 1, G, 30, 31, and 36 in Honey Creek Township, and sections 20, 21, 22, 29, and 32 in Montgomery Township. The pool is very irregular in shape, fingering out in several places, especially in the northeast part By T. E. Savage. WATER CONTROL, FLAT ROCK POOL 107 of the area. Its greatest width does not exceed three-fourths of a mile, and in some places it is considerably less than that figure. The pool is separated by barren territory from the Robinson and New Hebron pools in the north, from the Chapman and Parker pools on the southwest, and from the Birds pool on the south. The produc- ing area lies on the east slope of the La Salle anticline, but its long axis extends in a direction nearly at right angles to the trend of the main La Salle arch. During 1918 there were about 200 active wells in this area, which had an average daily production of about ?> T / 2 barrels. When the pool was first opened in 1910, productions of 100 barrels per day were not uncommon. Within one or two years after the wells were drilled, the production declined rapidly to near the present figures, and since that time the decrease has been very gradual. Geologic Section The rocks exposed in this area, or penetrated in deep drillings, consist of a mantle of unconsolidated materials composed of glacial till, loess, alluvium, and wind-blown sand belonging to the Quaternary series, overlying hard rock strata of Pennsylvanian age. QUATERNARY SYSTEM The glacial till in the Flat Rock area varies in thickness from a few inches to 20 or 30 feet, the average being about 18 feet. It is of Illi- noian age ; it is bluish when fresh, but weathers to a yellow or brown. As elsewhere, this till is somewhat sandy, consisting of unsorted clay, sand, pebbles, and boulders. The loess is a fine-grained, wind-blown silt which forms a sheeted deposit over almost the entire region, being thickest in the valleys, and thinner over the slopes and uplands. The alluvium consists of water- laid sand and clay, or mixtures of these, which in the larger stream val- leys of the region have a thickness of 50 to 100 feet. PENNSYLVANIAN SYSTEM Below the unconsolidated surface material the drill has penetrated Pennsylvanian strata to a depth of 900 or more feet, without reaching the base of the system. These consist largely of shale and sandstones, or more commonly of mixtures of these, with thin beds of limestone and coal. They represent the McLeansboro, Carbondale, and Pottsville formations, the latter containing the Robinson sand, which furnishes the oil and gas in the Flat Rock pool. 108 OIL INVESTIGATIONS A generalized section of the Pennsylvanian rocks in this area is given below: Table of Pennsylvanian rocks in the Flat Rock Pool McLeansboro formation Includes all of the Pennsylvanian rocks above the Her- rin (No. 6) coal; consisting of shales and sandstones and thin beds of limestone and coal. Thickness 450 to 500 feet. Carbondale formation Includes the strata between the top of the Herrin (No. 6) coal and the bottom of the Murphysboro (No. 2) coal; comprising shales, sandstones, thin limestones, and important coal beds. Thickness 300 to 400 feet. Pottsville formation Includes all of the Pennsylvanian rocks below the Murphysboro (No. 2) coal; consisting dominantly of sandstones, with gray and black shales, and a few thin coals. Thickness in adjacent areas 500 feet, not en- tirely penetrated in the Flat Rock pool. The following detailed log of the Selby and Cisler well No. 6, on the W. E. Ewing farm, near the center of the Flat Rock pool, will show more definitely the character and succession of the strata penetrated by the wells in the Flat Rock pool. This log was compiled from a study of the samples of drillings and from the driller's log, and is a repre- sentative record of the wells in this area. Log of Well No. 6 on Ewing Farm, section 31, Honey Creek Township Thickness Depth Pleistocene and Recent Feet Feet 1. Till and loess, yellowish brown with small pebbles 23 23 2. Clay, hard 2 25 3. Clay and sand, yellowish gray, calcareous; fresh water 8 33 4. Clay, yellow bluish brown, and gray, calcareous, with small pebbles 5 38 Pennsylvanian McLeansboro formation 5. Sandstone, gray, hard, shaly, calcareous 7 45 6. Shale, dark blue and gray, sandy, calcareous 20 65 7. Shale, black, hard, calcareous 2 67 8. Shale, black 35 102 9. Coal; some gas on top 6 108 10. Sandstone, white to gray, fine grained, shaly 4 112 11. Limestone, gray 33 145 12. Limestone, black 7 152 13. Limestone, blue and gray, granular 5 157 14. Shale, gray, sandy, calcareous 30 187 15. Shale, gray and dark 23 210 16. Shale, gray, calcareous 25 235 17. Shale, brown 15 250 WATER CONTROL, FLAT ROCK POOL 109 Log of well No. 6 on Ewing farm — Concluded Thickness Feet 18. Sandstone, gray, fine grained, with some shale (some water) 60 19. Limestone, gray, and shale with some sand 10 20. Shale, blue 10 21. Sandstone, gray, fine grained, with salt water.... 40 22. Shale, gray, hard 20 23. Shale, gray to dark brown, sandy 20 24. Shale, light gray 10 25. Shale, gray to brown 5 26. Limestone, light gray, shaly and sandy 5 27. Sandstone, fine grained, calcareous 10 28. Sandstone, dark, with some shale and limestone.. 45 29. Shale, gray to dark, with some sand and limestone 3 Carbondale formation 30. Coal (Herrin, No. 6 ?) 5 31. Shale, sandy, gray, fine grained : . 32 32. Limestone, gray, with some shale 15 33. Shale, dark gray, hard 35 34. Shale, gray and dark, soft 10 35. Shale, gray and dark, hard 30 36. Sandstone, yellowish, fine grained, calcareous (600- foot "gas sand" ) 20 37. Sandstone, gray to white, fine grained, water bear- ing 10 38. Shale, gray 30 39. Shale, black 20 40. Shale, gray, with sandstone, fine grained 15 41. Coal Little 42. Shale, light gray 40 43. Shale, gray to dark grayish brown 35 44. Shale, dark gray to brown, hard 1 45. Shale, blue gray, calcareous, with some fine sand.. 12 46. Shale, gray and dark, with coal 2 Pottsville formation 47. Shale, blue, with gray, fine-grained sand 70 48. Sandstone, dark gray to blue, shaly, calcareous, fine grained 23 49. Top of oil sand 50. Bottom of upper streak 51. Sandstone, gray, fine grained iy 2 52. Sandstone, yellowish gray, fine grained (oil pay) . . 8 53. Sandstone, gray, fine grained (water sand) 5 54. Shale, blue 1 55. Sandstone, gray fine grained, with a few larger grains (water sand) 10 Depth Feet 310 320 330 370 390 410 420 425 430 440 485 488 493 525 540 575 585 615 635 645 675 695 710 750 785 786 798 800 870 893 905i/ 2 909% 911 919 924 925 935 110 OIL INVESTIGATIONS TOTTSVILLE FORMATION The Pottsville, which is the lowest formation of the Pennsylvania!! system, has not been entirely penetrated by the deep wells in the Flat Rock pool. From the logs of wells in adjacent territory to the west and south, this formation is known to have a total thickness of 550 to 575 feet. The rocks consist chiefly of rather massive sandstones, which merge into sandy shales in the upper part. A few thin coals are present at different levels. The stray gas sands that are found in this area are thought to occur in the upper part of the Pottsville formation. The Robinson sand, which furnishes the oil in the Flat Rock pool, lies about 100 feet below the top of the Pottsville. Below the Robinson sand the sandstones in the lower part of the formation are usually filled with water. CARBONDALE FORMATION The rocks of the Carbondale formation, like those of the overlying McLeansboro, are dominantly sandy shales, but they also include beds of micaceous sandstone, thin limestone, and important coal beds. The most prominent members of the formation are the Herrin (No. 6) coal at the top, the Flarrisburg or Springfield (No. 5) coal 50 to 60 feet below the Herrin bed, and the Murphysboro (No. 2) coal at the base. The so-called "gas sand" occurs near the middle of the formation. The total thickness of the Carbondale strata in this area is about 350 feet. MCLEANSBORO FORMATION A thickness of 40 feet in the upper part of the McLeansboro forma- tion is exposed in the vicinity of Flat Rock. These strata consist of 15 to 18 feet of yellowish-gray, rather thick-bedded, micaceous sandstone, often with a conglomerate 1 to 2 feet thick at the base, below which is a marked unconformity. In places this sandstone is underlain by bluish- gray shale which is in places obliquely jointed, and has a thickness of 12 to 14 feet. In other places in this vicinity the shale bed had been entirely cut out by erosion prior to the deposition of the conglomerate. Underlying the shale horizon is a gray, coarsely granular limestone, 2 to 5 feet thick, which is usually separated from an 18-inch coal bed by 1 to 3 feet of dark shale. Below this coal the deep wells usually penetrate gray and bluish or dark sandy shales interbedded with gray sandstones, shaly sandstones, and carbonaceous shale. In the lower part of the formation there occur with the shale and sandstone an occasional band of limestone and thin coal. The exposures of McLeansboro strata in this area show a number of low undulations, but in general they lie almost horizontal over the entire area. The total thickness of the formation in this region is 450 to 500 feet. Ill that -foot ■ange veils. feel. n by rs to part in a > Oil ome- 101th t of e of itted any were ; not flow. , IS itely lock iome own : the nd". •ring lat- • be- ■eful r 6B ini- *ting im- 110 syste: pool. this The sand level: in th furn top < lowe McL of n most at tl belo 1 The total tion 15 t( ofte: a m; graj" 12 t entii Unc 2 tc by : pen< sane of t bail' in t lie ; fori WATER CONTROL, FLAT ROCK POOL 111 The Producing Sands the 600-foot "gas sand" Near the middle part of the Carbondale formation is a sand that usually contains more or less gas, and is known locally as the 600- foot "gas sand". It varies greatly in thickness from place to place, a range from almost nothing up to 50 feet having been reported in different wells. This sand has a characteristic yellowish-brown appearance and oily feel. STRUCTURE OF THE SAND A structure map of the Pennsylvanian rocks in this area, shown by contours drawn on the top of the "gas sand" (Plate X), appears to indicate that the places where the sand is highest are in the southwest part of the pool, from which the surface of the sand declines rapidly in a northeast direction toward the Hope and Tohill farms of the Ohio Oil Company leases. Consistent with this structure the gas supply is some- what greater in the higher, southern parts of the pool than farther north in the area. The gas from this sand furnishes the greater part of the fuel used in pumping the oil in the entire Flat Rock pool. When the first wells were put down in this pool, the pressure of the gas was excessive, and difficult to control. Wells were often permitted to blow for days, and in some cases for an indefinite time, before any effort was made to stop the flow of gas. Even when the wells were plugged in accordance with legal requirements, the waste of gas was not prevented, as the sand and steel balls were not sufficient to stop the flow. UPPER SALT SAND The "Upper salt sand", also known as the "600-foot salt sand", is a slightly consolidated, water-bearing sandstone, occurring immediately below the "gas sand" and present over the entire area of the Flat Rock pool. The sand grains are commonly clean and white, containing some brownish feldspar, but the material is in strong contrast with the brown "gas sand" that lies above it. The water that causes the corrosion of the pipes and casings in this field comes from the "upper salt sand". The thickness of this sand ranges from 20 or 30 to 60 or more feet, being- greatest where the overlying "gas sand" is thin, and thin where the lat- ter sand is thicker. The drillers usually report no break or parting be- tween the "gas sand" and the "upper salt sand". However, by careful watching during the drilling of this part of the section in the Ewing 6B well, a thickness of 3 to 6 inches of hard shell parting was noted im- mediately above the water sand. It is possible that such a thin parting separates these sands in other parts of the Flat Rock pool. This im- 112 OIL INVESTIGATIONS pervious parting between the sand horizons doubtless would account for the fact that water from the wells that do not reach the bottom of the shallow "gas sand" is seldom actively corrosive, while the water from the oil wells that penetrate the underlying "upper salt sand" causes a great deal of trouble by its corrosive action in the casing. This highly mineral- ized water from the "upper salt sand" attacks the well casings so rapidly that near the middle of the pool, where the trouble is greatest, the life of the casings may not be longer than 18 months to 2 years. It has destroyed an immense amount of casing and will ultimately cause the abandonment of the field before the complete drainage of the oil pool unless preventive steps are taken. FLAT ROCK SAND Practically all of the oil production in the Flat Rock pool comes from what is known in this area as the Flat Rock sand, the equivalent of the Robinson sand farther north and west. In this pool the sand is yellow- ish-gray and rather fine grained, and lies about 900 to 1,000 feet below the surface, the differences in depth being largely due to the relatively rapid thinning and thickening of this bed. The larger part of the oil comes from a depth of 925 to 950 feet. This sand appears not to be continuous over the entire Crawford County oil field, but occurs as dis- connected lenses of different sizes, shapes, and thicknesses irregularly spread over the region at a fairly well-defined horizon. It is most con- spicuously irregular in the northeast and the southwest portions of the Flat Rock pool. In the Montgomery Township area the sand occurs in three lenses each of which contains oil, but only the lowest furnishes paying production. The upper surface of the sand seems to present a succession of ridges and depressions which in general extend parallel with the long axis of the pool. The ridges and several of the depressions are shown on the structure map, Plate XI. It is significant that the strongest well in the Flat Rock pool is located on one of these ridges. This is the Selby and Cisler well No. 8 on the Ewing farm. The pay portion of the Flat Rock sand is usually immediately under- lain by water and is commonly only 3 or 4 feet thick. However, the logs of some of the wells, notably those on the central Tohill farm, indicate a thickness of 70 feet for this sand. In some of the wells located over depressions in the sand, the drill passed into the water sand without encountering any oil pay. The salt water that is present immediately beneath the oil pay, from which it is not separated by a parting of any kind, was evidently instrumental in the collection of the oil, and it rises higher into the WATER CONTROL, FLAT ROCK POOL 113 oil sand as the oil is exhausted from above it. When the pool was first drilled, the head was so strong in some of the wells that the water rose and flowed out over the top. In drilling wells at present the greatest care is necessary not to penetrate so near to the water sand that the shot of nitroglycerine will break into this sand and flood the well with more water than the pumps can handle. In such an event the only remedy is the use of cement to close up the pores and cracks in the water sand, and so shut off the flow of water, a solution only slightly less corrosive than that from the "upper salt sand". This method of control of the lower water is eminently successful in all cases where it has been used with proper pre- cautions in the process of cementation. STRUCTURE It may be seen from the structure map on which the contours are drawn on the Flat Rock sand (Plate XI) that this sand appears to be lenticular, the lenses extending in long narrow belts having a general northeast-southwest trend. The slope on the southeast side of the ridges is rather regular and gradual, while on the northwest side the sand fingers out in irregular, lobate extensions. The depression contours on the west side also appear markedly different from those in the east side. Mr. Rich 1 has suggested that in the Flat Rock pool the oil-bearing sands may be a part of a great delta formation in which are combined river-channel deposits, shore or barrier beaches, thrown up by waves in front of a delta, and wave-worked sand spread out upon the adjacent ocean bottom. By this explanation the Flat Rock sand would appear to represent off-shore or barrier beaches built up by the waves along a delta front. The trend of the axes of the minor ridges and depressions, parallel with the long axis of the pool, is consistent with this explanation. The gradual slope on the east and the minor depressions on the west are also in harmony with such an explanation. The more or less irregular char- acter of the contours on the west, while those on the east are confined to larger curves, can also be explained on the assumption of an irregular lens of sand. In the Flat Rock pool as a whole the top of the Robinson sand lies from 30 to 50 feet higher than the level of this sand in adjacent areas, a feature which was due in part at least to deformation. The character of the surface with its parallel ridges and its fingering lenses is such as to indicate that these local irregularities of the sand are due to its mode of deposition, rather than to deformation after the material was deposited. ir Rich, John L., Oil and gas in the Birds quadrangle. 111. State Geol. Survey Bull. 33, p. 137, 1916. 114 OIL INVESTIGATIONS OIL CHARACTERISTICS. The oil from the Flat Rock pool has rather high specific gravity and sulphur content, although the variation is considerable even in the small area under consideration. One well, No. 12 on the L. N. Tohill farm, sec. 31, Honey Creek Township, shows a gravity as low as 30.5° Beaume, while well No. 27 on the W. E. Ewing, section 31, E. Honey Creek Township, has a gravity as high as 18.4°. A few scattered samp- lings determined the fact that there was considerable variation, and the work was continued to bring to light any regularity, if such did occur. A sample was taken from every well and carefully warmed and the gravities taken. When these were plotted, so marked appeared the tend- ency for the lighter oils to find their way to the center of the pool that a contour map was based on the gravities alone (fig. 21). This map showed that the lighter oils were restricted almost entirely to the center of the pool, though the heavier oils would occasionally be found there also. There are two possible explanations for the occurrence 1 : First, the lighter oils may have migrated bodily to the upper portions of the pool. This is unlikely since petroleum is a solution of different constituents mutually dissolved, and solutions will not separate gravitatively. Second, through change of temperature or pressure, the gaseous hydrocarbons may have been released from the oil and migrated as gas along the top of the sand and reabsorbed. The action would not be uniform and would be incomplete, but the tendency would be to move the gases to- ward the higher portion of the pool. If this is the case, the difference is due only to the presence of more dissolved gases in the center of the pool than upon its flanks. This is supported by the fact that the wells that produce "lively" oil are mostly found in the central portion. The only certain test would be a chemical analysis to see if the difference was a major one, involving the constituents of the heavier oils, or a minor one affecting only the gaseous part of the series. WATER CHARACTERISTICS The corrosive waters of the Flat Rock pool are of two varieties, the upper water is the more active of the two, and it differs essen- tially from that of the lower sand. Analyses were made of the waters, both in the laboratory and field by the Illinois Water Survey, as shown in Table 9. The upper water is high in chlorides, sodium, potassium, calcium, and magnesium. The lower water is high in sulphates and lower in the alkali and alkaline 1 Rich, J. Li., Oil and gas in Birds quadrangle: 111. State Geol. Survey Bull. 33, p. 139, 1916. 15 £ 0> & re in lost ork hat ms- ater WATER CONTROL, FLAT ROCK POOL 115 fT 21.9 & tfi?"" gP ^ » , / / / 24.2 ' 24 > L N. TOHILL X «<"^^ - — — "^ \ 24 2 244 24.7 I 2 i 2 «^ DA REAVILLE/ • • 25.0/ m 24 'jf •/ • / J. D. REAVILLE 22^13 J .D .REAVILLE zzi > ^: & Fig. 21. Map showing contours on Beaume oil gravities. The lighter oils are in the higher parts of the structure. (Compare Plates X and XI.) earth chlorides. The total of dissolved salts in the upper water is almost twice that in the lower. The hydrogen sulphide content is similar. The chemical reaction is somewhat complicated 1 , and research work has not as yet been completed. The iron is dissolved in a somewhat complex reaction and precipitated as a sulphide. It is carried in sus- pension to the water-receiving tanks and there deposited. * Unpublished report on corrosive reactions by W. F. Monfort of 111. Water Survey. 116 OIL INVESTIGATIONS o I r © o co oo tf . % ft o ft ^ H— , OJ CO Sh Sv. ctf xu ft o fc 6 d* o 2£ I r o o co q °°d d d o5 o J A J «B ■* 00 lo Cxi q o eo ui - rl N H O >jC5 o oo W H KJ LO o -^ >> O ^ ft 0) c r/) rt d 0) cd >i l« o 0) o St 1§ be o .5 £ CD s s a) a> ^ ft,* o M o cd ^ cd ft cd ft -"-» 5 ■+-> 0) O o> m ■A m a a a Cd cd Cd rf +-> -i_> +J Ci rH OO h » -d * CD £ * 0JD 2 15 cd o -e s ^ s WATER CONTROL, FLAT ROCK POOL 131 TESTING TO DETERMINE SOURCE OF INCOMING WATER Use of Venetian Red as an Indicator Well No. 7 of the Selby and Cisler Company, on the W. E. Ewing lease, had a packer set on tubing in the lower portion of the 6 y^ -inch string. This string had been corroded sufficiently to let in the upper water. In order to get evidence as to whether the water in the well was from the bottom or was leaking around the packer, water was run into the casinghead, and Venetian red (chiefly red oxide of iron) was poured into this connection along with the water. A watch was kept on the production to determine if any of the indicator got past the packer. The finely divided Ventian red being carried in suspension and not in solution would not be suitable for use as an indicator when the fluid had to pass through a sand or other filtering medium. As used for testing, the effec- tiveness of a packer when the water is entering the well in large volumes, or tests of a similar nature, Venetian red was considered satisfactory as a substitute for aniline dye, which was formerly imported and only to be ob- tained at a prohibitive price at the time of the test. In the case of this particular well, the dye was not pumped out. While such negative evi- dence even in this type of a case is not conclusive, it is a strong indication that the packer was holding. Use of Packers as a Testing Device Though packers are not recommended as a suitable device for per- manently excluding water from an oil or gas well, they are often useful as a temporary expedient, and as a testing device for determining the source of the water entering the well. By setting the packer in the bottom joint of the casing with the pump above and with a perforated nipple be- tween the packer and pump, a quicker and more positive test of the con- dition of the casing may be obtained. Of course, for such a method the bottom of the tubing must be plugged. When the casing seat is to be tested, a similar arrangement of perforated nipple, pump, and plug may be used, only the packer must be set below the bottom of the casing. By this method the test is made by pumping out the fluid from above the packer instead of from the sands. METHODS OF WATER CONTROL Use of Mud Fluid The use of mud fluid for controlling high-pressure gas wells and as a protection against the ill effects of unsystematic casing in nearby wells has been thoroughly discussed by Lewis and McMurray. 1 In the 1 Lewis, J. L., and McMurray, W. F., The use of mud-laden fluid in oil an< gas wells: U. S. Bureau of Mines Bull. 134, 1916. 132 OIL INVESTIGATIONS State of Illinois it is proposed to use mud fluid for two purposes — to arrest the corrosion of casing by water cased off back of it, and to avoid Pig. 31. Diagram to show the saving in casing accomplished by the use of mud fluid. the detrimental effects of unsystematic casing. The chemical and geo- logical aspects of corrosion have been described on a previous page. It remains now to consider the mechanical phases of the problem. WATER CONTROL, FLAT ROCK POOL 133 THE MUD To be most effective the mud fluid must consist of colloidal material, free from grit, sand, or lime cuttings. Such granular material tends to settle around the outside of the casing and to bridge or pack over the col- lars, not only interrupting the continuity of the column of mud fluid, but Fig. 32. Photograph showing the connection at the top of the well between the discharge of the mud pump and the casing in the circulation method. The outcoming mud fluid has been down through the casing, out its bottom, and is returning to the surface, outside the casing. possibly freezing the casing. If air is excluded from such a mud fluid, it will remain fluid indefinitely and with comparatively small amount of set- tling. The thicker the original mud fluid is used the less will be the sub- sequent settling. As general rule it is advisable to mix the mud as thick as the pumps will handle it. 134 OIL INVESTIGATIONS METHODS OF MUDDING WELLS Since the mudding procedure is identical whether the purpose is to obviate the necessity of three shut-offs, or to arrest corrosion, this discussion of methods if applicable to either case. There are, in gen- eral, three methods for mudding : 1. Jet the hole full of mud; insert and land the casing. 2. Run casing into the hole and hang the pipe a few feet off the bottom. Jet the pipe full of mud until the column equalizes inside and outside of the casing at the surface ; then set the casing. 3. Run casing into the hole and pump it full of mud. Make a closed connection between the discharge of the mud pump and the top of the casing, and continue pumping until the mud fluid descending in- side the casing and returning to the surface in the space between the casing and the wall of the hole is free from cavings, sand, or lime cut- tings, and is of the same specilic gravity as the ingoing fluid. (See figure 32.) Then land the casing. Whichever method is adopted, the mud fluid should not be bailed out of the pipe for at least 24 hours after completion of the job. A ditch or flume some 50 to 100 feet long should be arranged and the mud fluid run through it to afford apportunity for all coarse material to settle out (figs. 33-35.) It should terminate in a suction pit so placed that the suction line of the pump may be easily transferred from the sump to the suction pit when mudding operations are commenced. In the circulation process of mudding, when the mud returns to the sur- face outside the casing, it may frequently contain cuttings and cavings washed up from the hole; and therefore before it has returned to the suction pit it should be allowed to flow through the trench so that such coarse material may settle out. This ditch must be shoveled out at intervals. Frequently enough clean mud fluid for the job will be collected at the lower end of the mud sump. The necessary specific gravity may be obtained by providing an overflow so that the excess water which rises to the surface of the sump will run off. If sufficient clean mud is not collected in this way at the lower end of the sump, an additional supply may be obtained by drawing the clean mud fluid from the lower part of the sump and forcing it through a flexible discharge pipe into the coarser settlings at the upper end of the sump with which it is mixed. Thus the high-pressure stream of mud may be used as a hydraulic moni- tor, and, by circulating the mud fluid through the pump and ditch, all colloidal matter available is brought into suspension. WATER CONTROL, FLAT ROCK POOL 135 SUGGESTIONS WITH REGARD TO CASING As none but good casing should be mudded, it will stand having the joints well set up. The threads inside the coupling and on the ends of the casing joints should be thoroughly cleaned and threaded with lead and oil or some other suitable preparation before the joints are started. 4 long V_ -Receiving pit \ 3.5' wide leasing L 2dee P ^Barrel swing to guide discharge Pig. 33. Diagram showing the system used in collecting mud for mudding Selby- Cisler well, Ewing No. 6B. Whenever suitable tongs are available, the casing should be set up with the engine. By taking these precautions the strings will hang together and stand more severe stress in case jacks have to be used to free it dur- ing any future operation. When mudding casing by pump and circulation methods as de- scribed, it should be raised and lowered at intervals without interrupting the action of the pump. This vertical movement of the casing should not be less than 22 feet so that each coupling will pass the position form- erly occupied by the next above. This process tends to prevent ac- cumulation of debris on the wall of the hole which might cause the pipe to become collar-bound and to stick or ''freeze." While very little trouble has been experienced in other states in pulling casing which has been set with mud fluid, nothing but ex- perience can demonstrate whether or not such mudding operations will be as fortunate in this respect in Illinois. Nevertheless if experience should show that it is impossible to recover mudded strings of casing after prolonged standing, the operator will have been reimbursed many 136 OIL INVESTIGATIONS times for this loss of pipe, providing the mudding excludes upper water from the productive sands throughout the life of the well. It is on this argument that the use of mud is recommended in Illinois at the present time. Another precaution to be observed, especially in "spotty" territory, is to set the water string, drill into the pay sand, and if necessary to shoot the well before mudding. If then the well is to be abandoned, it is obviously unnecessary to mud the water string, but the mud saved for this purpose while drilling can be used to good advantage in properly plugging the hole. On the other hand, if the well shows up favorably when drilled into the sands, it is a simple matter to bridge the hole above the sands and lift the pipe, mud, and reseat the casing. APPLICATION TO REPAIR PROBLEMS CORROSION OF CASING AND METHODS OF PREVENTION There are areas in the Illinois pools where the rapid corrosion of casing necessitates frequent renewals. In some instances casing and well tubing must be replaced after two years' service. These replacement jobs are not only costly in themselves, but the financial loss is considerably augmented by the incidental loss of production both while the well is off and by the diminished output of the well when' returned to the producing status, an occurrence which frequently accompanies such water jobs. While this reduction in productivity is not universal, it is a very general characteristic of such troubles in other fields as well as those of Illinois. It has been observed that when water breaks into an oil or gas well, per- manent damage is frequently occasioned, and that the well will frequently not come back to its former productivity even after the water has been shut off. To prevent the corrosion of casing, two methods of procedure are open ; first, to use casing of such composition that it will not be corroded, and, second, to keep the corrosive agent from contact with the casing. Numerous efforts have been made by pipe manufacturers to supply non-corrosive casing, which have been but partly successful. As a rule such special casing is more costly than ordinary pipe. To keep the corrosive agent from contact with the pipe is the method of greatest promise at present. One way to achieve this is by filling the space between the casing and the wall of the hole with mud fluid and to set the casing so as to retain the mud in this annular space throughout the life of the well. This method, of course, did not originate with the present investigation, but merely constitutes the application of a well- known principle to a particular set of conditions. The method has been used successfully in many fields and depends for its success on two WATER CONTROL, PLAT ROCK POOL 137 properties of mud fluid — first, the clogging action of the fluid as it enters the interstices of a sand, which tends to convert the porous sand locally into an impervious sandy clay, and second, the static pressure exerted by the column of mud fluid, which will continually oppose the pressure tending to force water through the sand into the well and into contact with the casing. Suppose, for the sake of illustration, that a water sand penetrated at a depth of 1,000 feet is cased and mudded off by such a process as that subsequently to be described, and suppose that the specific gravity of the mud is 1.25, that is to say, 25 per cent heavier than pure water. Suppose also that the water has sufficient head to rise 600 feet in the hole, or within 100 feet of the surface. This head of water is equivalent to 260 pounds pressure per square inch. In opposition to this pressure of water tending to enter the hole is the Pig. 34. Photograph of the mud sump taken from the top of the derrick on Selby-Cisler well, Ewing No. 6B. pressure exerted by 1,000 feet of mud fluid, which exerts a counter- pressure of 511 pounds per square inch. Thus the pressure exerted by the mud tending to hold the water back is 281 pounds greater per square inch than the pressure of the water in the sand. The result is that some mud enters the sand, as stated, until sufficient resistance has been built up to balance the extra pressure of the column of mud and a state of equilibrium is obtained. By such a mud system, various fluids native to strata cased off are retained in their normal re- 138 OIL INVESTIGATIONS spective stratigraphic positions and are thus prevented from migrating up and down the hole to contaminate fluids of other strata. Also, if any of these fluids are directly or indirectly responsible for the corrosion of the casing, such corrosion is very likely to cease. One of the most striking facts in connection with the corrosion of casing in the Illinois fields is that the bottom joints of a water string rarely show corrosion when the casing is pulled. So general is this cir- cumstance that of the many oil men interviewed on the subject, not one had failed to observe it, and all attributed the fact to the protection af- forded by shale cavings from the hole which settled about this portion of the pipe. The use of mud fluid may therefore be considered as ex- tending similar protection throughout the full length of the string. INTERMEDIATE WATER AND ITS CONTROL In many oil fields there are areas where intermediate water is en- countered. By this term is meant a water-bearing stratum with pro- ductive oil or gas strata above and below it, and with "breaks" of im- pervious strata separating the several sands. When it becomes desir- able to produce from the lower productive stratum a competent opera- tor at once adopts means to protect the upper productive stratum from becoming flooded by the intermediate water, as would be the case if both the intermediate water and upper oil were cased off behind the same string of pipe. One method of doing this is the three shut-off system consisting of three strings of casing; one set above the upper productive strata and another below it, thus protecting it from upper and intermediate waters, while the third string is set above the second producing sand. This method is open to the following objections: It is costly, due to the extra strings of casing used, as well as the labor involved. It offers only temporary protection in contact with corrosive agents. If the first or second shut-offs fail before the third, the water will then spread in the upper productive sand and perhaps spoil adjacent wells produc- ing from it. Since under conditions of three shut-offs production from the lower sand in the offending well may not be diminished by the spread of water in the upper sand, the true source of the water may not be determined. Moreover, if the well at fault is making a good produc- tion from the lower pay an operator would be reluctant to pull the casing from such a well on a chance that the first or second shut-offs were at fault. Being only human, he might prefer to claim the benefit of the doubt rather than to risk spoiling a good well because of a suspicion that it might be causing damage to the upper sand. It is therefore of prime importance that first and second shut-offs, and for that matter, WATER CONTROL, PLAT ROCK POOL 139 every shut-off in drilling wells, should be made as nearly permanent as possible, having due regard for all factors and complications likely to arise in the future, as far as past experience may indicate them. It has been recommended to some of the companies operating where intermediate water is encountered, that one string of casing be thor- oughly mudded and landed above the lower pay ; and the other strings that might be necessary while drilling should be pulled, keeping fluid level of the mud outside the water string as near the surface as pos- sible at all times. Of course, in some cases, it will be advisable, for me- chanical reasons, to leave some conductor pipe in the hole in addition to the one string that is mudded. Such conditions are shown in figure 31, an Indian Refining Company well in the Petrolia district. To the left the well is shown as it would normally be cased, and to the right as •' _ ; '»..; !■'[.. >■■■'• ■■■•!' '' JS^S'yi ■ * ^' : '*W'^- -ife^'*"^ •? : ^ M :. ■■■ ' : Pig. 35. Photograph of the mud sump looking toward the derrick. Trench near the center in which coarse material settles out; suction and mixing pipes at the right, the former below the latter. it would be if mud fluid were used. The saving here is in the cost of the strings of pipe. Due to the pressure tending to collapse a string of pipe, which is exerted by a column of heavy mud fluid, old or very thin casing should not be used in mudding operations. Use of Cement Use of cement in oils wells is confined to repair work in so far as water control is concerned. 140 OIL INVESTIGATIONS The method of cementing off lower water as used extensively in the Illinois field, was first introduced by W. W. McDonald of the Ohio Oil Company. It is adapted to completed wells which have been drilled too deep, or in which the shot has introduced salt water, as well as to those which have been partially flooded as a result of the inevitable en- croachment of the water upon the field, due to extraction of the oil. MCDONALD METHOD OF CEMENTING BOTTOM WATER A string of two-inch tubing, plugged tightly with a wooden plug, is lowered to within a foot or so of the prospective top of the cement. Fresh water is run into the tubing until it is filled, and the bottom plug is knocked out with sucker rods or by striking the upper end of the water column. Fresh water is then allowed to run into the well for sev- eral hours to force any salt water back into the sands. Cement is in- troduced by the handful into the stream of water, preferably heated to 130°, until the amount desired has been put in. The water flow is con- tinued but in a smaller stream, merely enough to keep the circulation from the well outward, so as to hold the cement grains in the inter- stices of the sand, rather than from the salt reservoir toward the well, which would force the cement back into the well. The water flow should be kept up for six or eight hours. With ordinary cement the well should not be pumped sooner than the eighth day. There is a great difference in cements, and the cement used should be tested in a great excess of water before putting it in the well, to de- termine whether or not it can be depended on to set under such condi- tions. INDEX A PAGE Acknowledgments 22,52, 104 Adams County, geology and structure of 69-90 physiography of 71-72 stratigraphy of . 86-96 Agaricocrinns tuberosus, oc- currence of in Keokuk limestone 94 Alluvial deposits in Brown County 25 in Pike and Adams counties 86 Analyses of oil-well waters. .. .114-117 of Pike County gas 83 Archimedes, occurrence of in Warsaw formation 94 Artesian wells 86 Ava, drilling near 16-17 B Benville, Keokuk formation near 37 Bond County, drilling in 17 Brown County, physiography of 24 recommendations for drilling in 49-50 stratigraphy of 25-40 structure of 41-46 Burlington limestone in Brown County 38 in Goodhope and La Harpe quadrangles 53-59 in Pike and Adams counties 94 Bushnell, dome near 65 log of well at 56-57 PAGE Clinton County, drilling in.... 15 Coal City, seepage of oil and gas near 17 Coghill, John W. Jr., assistance of 52 Colchester coal, see No. 2 coal. Coles County, drilling in 12-13 Colmar-Plymouth fields, drill- ing in 16 Corrosion of casing, prevention of 137-138 Corrosive waters in Plat Rock Pool 111-113 Crawford County, drilling in.. 14 Cumberland County, drilling in 12, 18 D Devonian rocks in Brown County 38-39 in Goodhope and La Harpe quadrangles 53-59 in Pike and Adams counties 95 Douglas County, drilling in 18 Drilling, record of 18-20 E Echinoconchus alternates, oc- currence of in Keokuk limestone 94 Edgar County, drilling in 12 Edwards County, drilling in.. 17 Endothyra baileyi, occurrence of in Salem limestone.... 38 Ewing well No. 6, log of 108-109 C Calhoun County, Kimmswick- Plattin limestone in 96 Campbell Hill anticline, drill- ing on 16-17 Carbondale formation in Brown County 28-29 in Plat Rock Pool 110 in Pike and Adams counties 89-91 Casing, corrosion of 105 saving of by use of mud fluid 132 Central Refining Company, as- sistance of 104 Chestline, section near 91 Clark County, drilling in 12-13 141 ■ F Pair Weather, section near. ... 91 Fayette County, drilling in. . . . 17 "First lime" 38 Flat Rock Pool, geology of 106-113 peg model of 118-119, 121 water trouble in 106 Flat Rock sand 112-113 Fossils, occurrence of in Keo- kuk limestone 37, 94 in St. Louis limestone 31 in Salem limestone 33,93 in Warsaw formation 94 Friendsville Township, drilling in 14 142 INDEX— Continued PAGE G Gaging of wells in Flat Rock Pool 121-129 Galena-Platteville limestone, in Goodhope and La Harpe quadrangles 53-59 possibility of oil production from 61 Gallatin County, drilling in.. 16 Gas in glacial drift 66-67 in Pike County 75-84 "Gas sand", 600-foot, in Flat Rock Pool 110,111 Glacial drift, gas in 66-67 in Brown County 26-27 in Flat Rock Pool 107 in Pike and Adams counties 87 Gochenour well, log of 58-59 Goodhope Quadrangle, stra- tigraphy of 53-59 structure and oil possibili- ties of 51-67 H Hancock County, drilling in.. 16 Hazelwood, section near 93 Hoing sand 73-74 correlation of 39, 40 possibility of oil production from 60-61 in Goodhope and La Harpe quadrangles 53-59 I Illinoian till, distribution of 26-27, 87, 107 Illinois, rank of in oil produc- tion 9-10 structure of 63 Illinois oil, prices of 11 Illinois Pipe Line Company, as- sistance of 104 Indian Refining Company, as- sistance of 104 Jackson County, drilling in. J. and L. Parke well, log of. Jasper County, drilling in... Johnson County, drilling in. Johnson well, log of 16-17 47 12 16 47 K Keokuk formation in Brown County 37-38 in Goodhope and La Harpe quadrangles 53 in Pike and Adams counties. 94 PAGE Key horizons for Brown County 23-24 for Goodhope and La Harpe quadrangles 64 for Pike and Adams counties 72-73 Kimmswick-Plattin limestone in Brown County 39-40 in Pike and Adams counties 96 Kinderhook shale in Brown County 38 in Goodhope and La Harpe quadrangles 53-59 in Pike and Adams counties 95 L La Grange, section near 30 La Harpe Quadrangle, stratig- raphy of 53-59 structure and oil possibili- ties of ' 51-57 Lawrence County, drilling in.. 14 Lioclema, occurrence of in War- saw formation 94 Lithostrotion, occurrence of in St. Louis limestone 31 Loess deposits in Brown County 25-26 in Flat Rock Pool 107 in Pike and Adams counties 86-87 M McDonald method of cement- ing oil wells 140 McDonough County, drilling in 16 McLean County, drilling in. . . . 17 McLeansboro formation in Flat Rock Pool 110 Macoupin County, drilling in.. 15 Madden, Frank J., assistance of 104 Madison County, drilling in... 17,18 Maquoketa shale in Brown County 39 in Goodhope and La Harpe quadrangles 53-59 in Pike and Adams counties 95 possibility of oil production from 41, 61 Marion County, drilling in.... 15-16 May wells, logs of 48 Mink, Jerry, assistance of.... 71 "Mississippi lime" 38 Mississippian rocks in Good- hope and La Harpe quad- rangles 53-59 in Pike and Adams counties 92-95 Morgan County, drilling in. . . . 17 Morse, W. C, work of 22 Mount Sterling, Pottsville for- mation near 30, 31 St. Peter sandstone in well at 40 Mudding, methods of 134-135 Mud fluid, use of in water con- trol 132-138 INDEX — Continued 143 PAGE N Natural gas, see Gas. Nebel, M. L., work of 71, 104 Niagaran limestone, gas from 83-84 in Brown County 39 in Goodhope and La Harpe quadrangles 53-59 in Pike and Adams counties 95 possibility of oil production from 40, 41, 60 Northern Illinois, drilling in.. 17 No. 2 coal as key horizon in Brown County 23-24 in Goodhope and La Harpe quadrangles 63 in Pike and Adams counties 72-73 O Oakland, drilling near 13 Oil, character of in Flat Rock Pool 114 Oil-producing horizons ...40-41, 59-61 Ordovician rocks in Brown County 39-40 in Goodhope and La Harpe quadrangles 53, 61 in Pike and Adams counties. 95-96 P Packers, use of as indicator of source of water 131 Parke well, log of 47 Parrish well, log of 57-58 Pennsylvanian rocks in Brown County 28-31 in Plat Rock Pool 107-113 in Goodhope and La Harpe quadrangles 52 in Pike and Adams counties 89-92 Perry County, drilling in 17 Petroleum, prices of in 1916, 1917, and 1918 10-11 number of wells drilled for in 1917 and 1918 12,18-20 production of, 1905 to 1918. . 10 1917 and 1918 9-20 production of decreasing in Illinois 99 Pike County, drilling in 16, 76-80 geology and structure of.... 69-96 natural gas in 75-84 physiography of 71-72 stratigraphy of 86-96 Pittsfield-Hadley anticline 75-84 Plymouth field, drilling in 16 Plymouth oil, prices of 11 Pottsville formation in Brown County 30-31 in Pike and Adams counties 91 in Plat Rock Pool 110 possibility of oil production from 59 Productidae, occurrence of in Carbondale formation 90 Productus burlingtonensis, oc- currence of in Burlington limestone 94 Productus magnus, occurrence of in Keokuk limestone... 94 R Randolph County, drilling in.. 17 Recommendations for oil tests 49-50, 65, 84-86 for repair work 128 Repair work, use of cement in. 139-140 use of mud fluid in 137-139 losses resulting from delay of 129 recommendations for in Plat Rock Pool 128 Rich, J. L., work of 22, 23 Ripley dome 46 Robinson sand in the Flat Rock Pool " 110 Roseville. dome near 65 St. Louis limestone in Brown County 31-32 in Pike and Adams counties 92-93 St. Peter sandstone in Brown County 40 Salem limestone, fossils in.... 33 occurrence of in Brown County 24, 32-35 in Pike and Adams counties 93 Saline County, drilling in 16 "Salt sand, 600-foot'', see ''Up- per salt sand". Savage, T. E., work of.. 22, 33, 52, 83 Schuyler County, drilling in.. 16 "Second lime" 39, 73 Section of hard rocks in Brown County 27-28 in Goodhope and La Harpe quadrangles 52-53 in Pike and Adams counties 87-89 of Pennsylvanian rocks in Flat Rock Pool 108 Selby and Cisler Refining Com- pany, assistance of 104 Shinn, Claude, assistance of... 71 Single-barrel gage, description of 121 South central Illinois, drilling in 15-16 Southeastern Illinois, drilling in 12-14 Southern Illinois, drilling in.. 16-17 Spanish Needle Creek Dome, drilling on 15 144 INDEX— Concluded PAGK Spirifera, occurrence of in Keo- kuk limestone 94 Sporangites huronense, occur- rence of in Devonian shale 38 Staunton gas pool, decline of. 15 Stratigraphy of Pike and Ad- ams counties 86-96 Stronghurst, dome near 64 log of well at 55 Structure of Brown County 41-46 of Flat Rock sand 113 of "gas sand" in Plat Rock Pool HI of Goodhope and La Harpe quadrangles 63-66 of Pike and Adams counties. ..74, 75, 81-86 Structure, relation of to oil accumulation 43-44, 62, 73 Sweetland Creek shale in Good- hope and La Harpe quad- rangles 53-59 T Tests for oil, Brown County . . 46-48 Goodhope and La Harpe quadrangles 66 Three-barrel siphon gage, de- scription of 121-124 "Trenton limestone", see Ga- lena-Platteville limestone and Kimmswick-P I at t in limestone. PAGK u Upper Devonian shale in Brown County 38 in Goodhope and La Harpe quadrangles 53-59 in Pike and Adams counties. 95 "Upper salt sand'' in Flat Rock Pool 111-112 Venetian red, use of as indi- cator of source of water.. 131 W Wabash County, drilling in. . . . 14 Warsaw formation in Brown County 36-37 in Pike and Adams counties 93-^4 Washington County, drilling in 17, 18 Water, amounts pumped in Flat Rock Pool 128-129, 130 ill effects of on oil wells 104-106 Water control work, results of. 101-104 Water Survey, cooperation with 104 Well data for Pike County gas field 83-84, 76-80 Weller, Stuart, work of 22, 38, 71 Wells, flowing 86 Western Illinois, drilling in... 16