Press Bulletin Series Issued Twice Quarterly STATE OF ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION . -..■'-"" " A. M. SHELTON. Director Ul V 1J1V1\ V_T 1 I IE (TV !' STATE GEOLOGICAL SURVEY^ 1\ , J r - $& M. M. LEIGHTON. Cfee/; Urbana No. 6 ILLINOIS PETROLEUM December 4, 1926 THE SORENTO DOME By Alfred H. Bell Introduction All but one of the known oil and gas fields of southwestern and south- central Illinois lie within a rectangle 70 miles long and 18 miles wide, extend- ing in a northwesterly direction from Centralia to Carlinville. (See fig. 1.) Practically without exception they are situated upon, or are closely related to, well-defined anticlinal structures. In order to reduce as much as possible the risk involved in prospecting for oil in this territory, drilling should be preceded by (1) a search for favorable structures hitherto unknown and i '.' | a reconsideration of the data relating to known favorable structures. This paper gives briefly the results of a restudy of the Sorento dome in parts of Madison, Montgomery and Bond counties. In a former publication 1 the dome was represented by contours indicat- ing the elevation above sea level of Elerrin (No. 6) coal and having an interval of 50 feet ; it is here represented in greater detail by contours on the same key bed having a 10-foot interval. A restudy of the data has shown that what has been known as the "Sorento dome" really consists of two parts. In this report these will be referred to as the New Douglas dome, which centers about a well in NE. 34 sec - 10> T. 6 N., R. .5 W., and the Panama anticline which lies about 1 mile west-southwest of Panama. Stratigraphy An outline of the stratigraphic section for the Sorento dome area is given in table 1 . The data have been taken partly from the column given by Wallace Lee 2 and have been partly compiled from a study of well logs. It will be noted that there is considerable disagreement between the pre- Mississippian section as interpreted in this report and the section given by Lee. 1 Blatchley, R. S., Oil and gas in Bond, Macoupin, and Montgomery counties, Illi- nois: Illinois State Oeol. Survey Bull. 28, PI. II, 1914. 2 Lee. Wallace, U. S. Oeol. Survey Geol. Atlas, Gillespie-Mount Olive folio (No. 220), p. 3, 1926. 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The St. Peter sandstone was not reached in the Mark Flitz well which finished in the Kimmswick-Plattin limestone, 315 feet below its top. In drilling wildcat wells, the efficiency of drilling is limited by a lack of knowledge of the depth and exact character of the beds to be penetrated. Lateral variations in thickness and lithologic character of the strata as well as the dip of the strata are the factors to which this lack of knowledge is due. In order to minimize the difficulty, an estimated depth to the top of each formation which would be encountered in a well drilled near the top of the New Douglas dome is included in the stratigraphic table. The esti- mated depths are based on the logs of several wells, of which the deeper ones are located farther from the top of the structure than are the shallower ones ; consequently they are likely to be more nearly correct for the upper than for the lower formations. Thus the deepest well in the area, which reached approximately the base of the Osage, is located on the Smith farm, sec. 15, T. ? N., R. 5 W., 4 1 miles north of the top of the structure. The nearest well that reached the Kimmswick-Plattin ("Trenton") is 9 miles north; the nearest well that reached the St. Peter sandstone is 16 miles northeast. Structure Structure is represented on the accompanying contour map (fig. 2) by contours which give the elevation above sea level of Herrin (No. 6) coal or, in case this coal is absent, of its probable stratigraphic horizon as inferred from the correlation of other beds. Table 2 gives the data on which the contours are based. On account of the superior information given by core drilling, the logs obtained can in most cases be readily correlated with each other and it is believed that considerable reliance can be placed on structure maps which are based on such logs in areas where the wells are relatively closely spaced. The logs of the churn drill wells in this area, on the other hand, are not easily correlated with each other or with the logs of diamond drill coal test wells. They have, therefore, not been considered in the con- struction of the accompanying map (fig. 2). The elevations of wells in T. 6 N. were determined by stadia survey by the writer's party with the exception of the wells in sees. 23 and 24, T. 6 N., R. 5 W., and sec. 20, T. 6 N., R. 4 W., for which the elevations were determined by aneroid. The elevations of the wells in T. 7 N. and in sec. 2, T. 6 N., R. 4 W.. were Lee, Wallace, op. cit., p. 3. For the log of this well, see Lee, Wallace, op. cit., p. SOEENTO DOME 5 taken from various sources and, with very few exceptions, they had been obtained originally by stadia survey. The map shows the two rather distinct parts of the Sorento dome referred to in the introduction to this report. The top of the New Douglas dome lies approximately in sec. 10, T. 6 N., R. 5 W. ; the highest part of the Panama anticline lies west-southwest of Panama (sec. 22, T. ~i N., R. 4 W.). It is probable that a continuous anticlinal axis connects these two structural highs. The determination of the entire upper part of the structure of the New Douglas dome depends on the interpretation of the log of one well (Map No. 25, Ameling No. 4. sec. 10, T. (J N., R. 5 W.) and this log shows the absence of Herrin (No. 6) coal, the bed on which the contours of figure 2 are drawn. In order to determine the stratigraphic horizon of this key bed, a cross-section of two wells ( Nos. 25 and 19) and one mine shaft (No. 27) was drawn (fig. 3). The evident correlation of the other beds, as shown in the cross-section, places the horizon of the top of the coal very definitely as indicated and there seems to be little room for doubt as to the accuracy of this interpretation. Figure 3 shows a dip of more than a hundred feet from well No. 25 to the mine and the dips from the center of the structure in all directions ex- cept to the northwest ( as shown in figure 2 ) appear to be fairly well authenticated. Development Six churn drill wells have been drilled in the area, of which all but two were unfavorably located with respect to structure. Each of the other two was within a mile of the anticlinal axis (sec. 20, T. 7 N., R. 4 W., and sec. 35, T. ~, N.. R. 5 W.). Only a very incomplete record of the latter is avail- able. It gives Herrin (No. 6) coal from 325 to 332 feet and sand from 610 to 700 feet ; the sand is probably Pottsville. The first well has the following sand record : Feet Sandy shale 325 to 370 Sand 660 to 690 ( probably Pottsvillo ) Sandy shale 690 to 710 Sandy shale 736 to 765 The St. Louis limestone ("Mississippi lime") was topped at 765 feet. The casing record was as follows : 10-inch 20 feet S^-inch 402 feet 6%-inch 695 feet A well in sec. 15, T. 7 N., R. 5 \\\, had a showing of gas in a sand at 586 feet and a showing of oil lower in the same sand from 5S I to 618 feet. ILLIXOIS PETROLEUM Table 2. — Well data from Sorento Dome area "Map Company Well No. Surface Elevation Feet No. 6 coal No. Depth Elevation Feet Feet 1 Whitebreast Fuel I 611 458 153 2 Whitebreast Fuel M 519 360 159 3 591 377 214 4 Whitebreast Fuel E 527 295 232 5 Whitebreast Fuel F 525 353 172 6 Shoal Creek Coal 538 374 164 7 Whitebreast Fuel 1 563 446 117 8 Whitebreast Fuel L 609 459 150 9 Lumaghi Coal 10 593 387 206 10 A. W. Crawford 20 522 294 228 11 Sorento Coal 585 384 201 12 Lumaghi Coal 7 584 400 184 13 Lumaghi Coal 26 595 415 180 14 650 390 260 15 640 395 245 16 Lumaghi Coal 1 600 364 236 17 Lumaghi Coal 5 582 373 209 IS Lumaghi Coal 4 589 373 216 19 Sorento Options 22 589 351 238 20 Lumaghi Coal 590 340 250 21 Wilmington Star Coal 585 342 243 22 H. R. Ameling 6 592 357 235 23 H. R. Ameling 9 591 234 257 24 H. R. Ameling 15 613 356 257 25 H. R. Ameling 4 580 285 295 26 H. R. Ameling 1 577 374 203 27 Big Mound Coal 605 415 190 2S H. R. Ameling 16 609 372 237 29 New Staunton Coal 10 609 370 239 30 H. R. Ameling 7 572 347 225 31 New Staunton Coal 13 566 332 234 32 New Staunton Coal 11 600 396 204 33 H. R. Ameling 20 596 400 196 34 H. R. Ameling 8 591 397 194 35 Schallenberg 614 437 177 36 H. R. Ameling 3 565 370 195 37 Whitebreast Fuel H 511 362 149 38 Duncan 3 577 441 136 39 Sullivan Machinery 1 576 444 132 40 Shoal Creek Coal 2 574 443 131 41 Consolidated Coal 2 506 363 143 42 Consolidated Coal 1 528 378 150 See figure 2 for locations. SOKENTO HOME Z oi H i)\ ^mWlllr 2vJH ILLINOIS PETROLEUM Elevation in feet . _ 600, 19 27 500 400 ss 300 200 100 100 J 53=FS 25 Herrin (ko.G)coal \ \ \ \ \ \ Herrin _ v (No. 6) coal Shale, surface material EEE^ Sandy shale \ ■ ■ -.| Sandstone •fr-M Limestone r^tttl Sandy limestone .^ Coai ^=^| Bituminous shale \xxx xl Fire clay Salt water X X X X 33 3 miles Fig. 3. Cross-section through New Douglas dome. See fig. 2 for locations of wells and mine shaft. (By A. H. Bell, Illinois State Geological Survey.) SOKENTO DOME » This sand probably belongs in tbe Pottsville and may be contemporaneous with the producing sand of the Staunton gas field. Recom mendations The most important oil production in southwestern Illinois is from sands of Chester age, and the probability of the presence of Chester sands over the New Douglas dome is a favorable feature from the point of view of the oil prospector. A study of the logs shows that Chester rocks are present in all the wells shown on the map that have been drilled to a sufficient depth and it is there- fore highly probable that the Chester is present on top of the New Douglas dome. The following table lists these wells with the thickness of Chester found in each : Taisle 3. — Wells in Sorento Dome area penetrating the Chester Location Thickness of Chester Section Township N. Range W. Feet 15 7 5 80 24 7 5 80 20 7 4 80 24 6 5 125 15 6 4 record incomplete It should be added, however, that from general studies of the surround- ing region, tbe Chester is known to thin out to the west and to thicken to the east. The Chester is definitely absent in the Staunton gas field, so that tbe western boundary of the area in which Chester rocks are present lies somewhere between the westernmost wells listed above, and the Staunton dome area — its precise location is not known. Although it is not absolutely certain, yet it is very probable that Chester rocks occur on top of the New Douglas dome. Besides the Chester there are several other possible producing horizons. (See table I, which lists the producing horizons in other oil and gas fields of central and western Illinois. 5 ) Of these perhaps the most important is the Pottsville, since to it belong the gas sands of the Staunton and other fields to the north. Xo production from rocks older than the Chester has been obtained within a radius of 50 miles. A showing of oil, variously reported from 10 to 75 barrels, was obtained in Brown Xo. 1. sec. 9, T. .") N., R. 1 W., six e figure 1 for the Locations of most of these fields. 10 ILLINOIS l'KTROLKVM miles south of Sorento. This oil was from a sand of Devonian or Silurian age at a depth of 2000 feet. The well did not make a commercial producer and a number of dry holes were drilled in the vicinity. It seems probable that once the top of the St. Louis limestone is reached the most likely oil-bearing strata have been penetrated. The advisability of deeper drilling is open to question. If it is desired to test the structure very thoroughly, drilling might be continued to the top of the Kimmswick-Plattin Table 4. — Producing horizons in central and western Illinois oil and gas fields Depth Feet 285 610 690 1810 2510 Horizons 1. Pennsylvanian sands below Her- rin (No. 6) coal 2. Chester Remarks Produce oil at Junction City and Wamac; oil and gas at Carlin- ville; gas at Staunton. Oil at Progtown, Carlyle, Sandoval and C e n t r a 1 i a ; gas in Bond County, (1) A y e r s, and (2) Lindly. 3. Ste. Genevieve (upper part of Oil in Lawrence County. "Mississippi lime"); correlated with "McClosky sand" 4. Devonian or Silurian 5. Silurian: "Niagara lime" Hoing sand. and 6. Ordovician: Kimmswick-Plattin limestone ("Trenton lime- stone") Showings of oil in wells in Old Ripley Township (south of Ayers anticline). Gas in Pike County (Pittsfleld- Hadley anticline), and oil at Colmar. Oil at Waterloo. ("Trenton"). The possibility of oil in commercial quantities at still greater depth is decidedly remote. On the whole it seems a better procedure to drill only into the St. Louis ("Mississippi lime") and if the first test to this depth is unsuccessful to drill the structure in another place in the hope of finding more favorable sand conditions. Further testing would be especially desirable if encouraging showings are found in the first test. SORENTO DOME 1L Assuming that an oil sand exists in the region having a structure similar to that shown for Herrin (No. 6) coal, the most probable location of oil pools therein is in the upper parts of the New Douglas dome and the Panama anticline. On account of the lack of proof for any reverse dip the Panama anticline does not seem to be as favorable a structure for oil accumulation as the New Douglas dome, but at the same time it should be noted thait because of the lack of drilling, the structure in the area to the west of the Panama anticline is not well known. If production is secured from the New Douglas dome it would be desirable to test the Panama anticline as well, making a location not far from its summit as shown in figure 2 (sec. 28, T. 7 N., R. 4 W.). If, however, oil sands exist in the region in those lower strata which are. separated from Herrin (No. 6) coal by one or more important unconformi- ties, the relations of the possible oil pools to the structure of Herrin (No. 6) coal are not likely to be so simple. This was found to be true for the Lange- wisch-Kuester and Brown pools east of Centralia where the production, coming from a sand in the lower part of the Chester, is found on the slopes of the anticlinal structures in Herrin (No. 6) coal." Hence, the possibilities of production in a region cannot be said to be exhausted even when the upper parts of the anticlines in Herrin (No. 6) coal have been tested. At the present time definite recommendations based on adequate knowl- edge of the structure of pre-Pennsylvanian strata in southwestern Illinois in general and in the Sorento dome area in particular cannot be made. In the future, as knowledge of these deeper strata gradually accumulates, and as more accurate data are obtained from more carefully kept logs, the geological guidance of oil prospecting will be of greater service than is at present possible. Conclusions The New Douglas dome is a structure with more than the usual amount of closure, situated in a region in which oil and gas have been produced from structures having less closure. The upper part of the structure has not yet been tested for oil. The presence of a number of sands of Pennsylvanian age upon the dome has been demonstrated, and it is probable that Missis- sippian sands are also present. In view of (1) the unusually favorable structure, and (2) the presence of possible reservoir sands, it is recom- mended that one or more test wells be drilled in this area. 8 Bell, A. H., Oil investigations in the Centralia area — preliminary report: Illinois State Geol. Survey Press Bulletin Series, Illinois Petroleum No. 4, pp. 6-10, August 28, 1926.