14.GS: 
 CIR 287 
 c. 1 
 
 STATE OF ILLINOIS 
 
 WILLIAM G. STRATTON, Governor 
 
 DEPARTMENT OF REGISTRATION AND EDUCATION 
 
 VERA M. BINKS, Director 
 
 Clay Mineralogy 
 
 of Pre-Pennsylvanian Sandstones 
 
 and Shales of the Illinois Basin 
 
 Part II. — Clay Mineral Variations Between 
 Oil-Bearing and Non-Oil-Bearing Sandstones 
 
 Thomas W. Smoot 
 Kedar Narain 
 
 DIVISION OF THE 
 
 ILLINOIS STATE GEOLOGICAL SURVEY 
 
 JOHN C.FRYE, Chief URBANA 
 
 CIRCULAR 287 
 
 1960 
 
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Clay Mineralogy of Pre-Pennsylvanian 
 Sandstones and Shales of the Illinois Basin 
 
 Part II. — Clay Mineral Variations Between 
 Oil-Bearing and Non-Oil-Bearing Sandstones 
 
 Thomas W. Smoot and Kedar Narain 
 
 ABSTRACT 
 
 The clay mineral compositions of approximately 70 samples 
 of oil-bearing and non-oil-bearing sandstones from the Mississi- 
 ppian Chester Series of the Illinois Basin were determined. Part 
 of the samples are from nine Chester formations located throughout 
 thedeep part of thebasin;the others are from the Aux Vases Forma- 
 tion in a limited area in Hamilton County. 
 
 Easily discernible differences between the compositions of 
 clay minerals from oil-bearing and non-oil-bearing sandstones, 
 apparent in both randomly chosen samples and closely associated 
 samples, are thought to be partly a function of the presence or 
 absence of hydrocarbons. Studies of these differences may be of 
 use in the investigation of the time and mode of oil accumulation. 
 
 INTRODUCTION 
 
 This report is the second in a series based on a study of approximately 70 
 clay mineral analyses of outcrop and core samples of pre-Pennsylvanian sandstones 
 and shales of the Illinois Basin. About eighty percent of the samples were from nine 
 formations of the Chester Series of the Mississippian System; the others represent 
 the Valmeyer Series (Mississippian) and the Ordovician and Cambrian Systems. 
 
 This report differentiates between the clay mineral suites from oil-bearing 
 and non-oil-bearing sandstones and presents possible explanations for, and the 
 significance of, the differences by comparing the clay mineral assemblages with 
 those commonly found in associated shale facies. 
 
 The report is the result of essentially two separate investigations. The 
 first was a study of the clay mineralogy of core samples representing nine Chester 
 formations from locations throughout the deep part of the Illinois Basin (the Fairfield 
 Basin). The second was a study of the Aux Vases Formation (Chester Series) in three 
 closely related oil fields in approximately 30 square miles in Hamilton County, 
 Illinois, in the central portion of the deep part of the basin. 
 
 This report is based in part on a thesis by T. W. Smoot submitted in partial 
 fulfillment of the requirements for the degree of Doctor of Philosophy in geology and 
 in part on a thesis by K. Narain submitted in partial fulfillment of the requirements 
 for the degree of Master of Science in geology, both in the Graduate College of the 
 University of Illinois, 1959. 
 
 The authors express their appreciation to Professor R. E. Grim for advice 
 given during all stages of the study. 
 
 [1] 
 
ILLINOIS STATE GEOLOGICAL SURVEY 
 
 SELECTION OF SAMPLES 
 
 (Tayeite" ~ effinghamL . 
 
 3ND " I 
 
 h 
 
 rciii 
 
 i'mahio'n 
 
 "L. 
 
 .CRAWFOBD 
 
 RICHIAND I IAWRENCE 
 
 WASHINGTON 
 
 "I 
 
 >JEFFERSON 
 
 f 
 
 U~ '.WABASH. 
 
 Forty-six samples represent- 
 ing nine formations of the Chester 
 Series (Mississippian System) from 39 
 locations scattered throughout the 
 deep part of the Illinois Basin (the 
 Fairfield Basin) constitute the basis 
 for part of this report (fig. 1). The 
 samples were chosen to represent the 
 largest geographical distribution of 
 time-rock units using a limited num- 
 ber of samples and to afford compari- 
 sons of the clay mineral suites of 
 approximately contemporaneous oil- 
 bearing and non-oil-bearing sand- 
 stones and associated shales. 
 
 In addition, 26 core samples 
 from 21 locations of the Aux Vases 
 Formation came from the southwest 
 portion of the Bungay Consolidated 
 Pool, the northeast portion of the 
 Dale Consolidated Pool, and the 
 Thackeray Pool (fig. 2) in Hamilton 
 County, Illinois. All of the samples 
 were taken from the lower part of the 
 cores available so that, as far as 
 possible, they were from the same 
 stratigraphic position. Both sand- 
 stones and shales were sampled so that 
 any lateral facie s present were represented 
 
 As explained in Part I, the central portion of each core was carefully sepa- 
 rated from the outer portions and used as the sample in order to minimize contami- 
 nation by drilling-mud invasion. 
 
 Fig. 1 - Location of Chester samples 
 from the Illinois Basin, with the ex- 
 ception of Aux Vases samples from 
 Hamilton County (cross-hatched). 
 
 SAMPLE PREPARATION 
 
 The preparation of the non-oil-bearing sandstone and shale samples is des- 
 cribed in detail in Part I. The oil-bearing sandstone samples were prepared in a 
 manner somewhat different from that used for the non-oil-bearing and slightly oil- 
 bearing sandstone samples. 
 
 In order to remove the oil from oil- saturated sandstone samples, they were 
 crushed, washed in a Soxhlet extractor with low-boiling petroleum ether for periods 
 ranging between 20 and 48 hours, and then air dried at temperatures slightly higher 
 than room temperature (30 to 34 C) until the petroleum ether had apparently evapo- 
 rated. These samples were further disaggregated and treated the same as the non- 
 oil-bearing samples (Part I). 
 
 CLAY MINERALS PRESENT 
 
 A detailed description of the clay mineral groups and subgroups encountered 
 in the samples appears in Part I of this series. It is convenient, however, to 
 
CLAY MINERAL VARIATIONS 
 
 KEY 
 + Non- producing oil well 
 • Producing oil well 
 
 Scole 
 
 
 
 
 
 
 1 
 
 
 
 
 Bungay 
 
 356 
 + 
 
 i 
 
 
 
 
 
 1631 
 
 + # 
 
 1779 
 
 
 
 784 # 
 
 
 
 •1936 
 
 + 
 1529 
 
 
 
 O '/2 1 2 3 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 i 
 
 
 
 
 
 
 1 
 
 Thackeray 
 
 iZ"J 
 
 
 + 
 
 466 
 
 
 
 
 
 Mc 
 
 Leansbor 
 
 n 
 
 4 
 
 J 
 
 
 1581 
 + 
 1545 • 
 
 19 35 • 
 • 1601 
 
 + 1934 
 
 
 
 
 I 
 
 i 
 
 i 
 i 
 
 
 
 
 
 1694 
 
 1765 
 
 + 
 
 
 
 
 
 
 
 
 
 
 + 
 1755 
 
 1629 
 
 + 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 r 
 
 
 
 
 ,2399 
 
 l # 730 
 
 + 
 
 2315 
 
 
 
 
 j 
 
 
 
 
 
 
 
 
 
 
 
 — i 
 
 
 1940 
 
 + 
 
 
 
 
 620 
 
 • 
 
 
 
 
 
 i 
 
 
 
 
 
 
 "" U 1 
 
 Dale 1 
 
 
 
 
 
 < 
 
 ! 
 
 R.6E. 
 
 R.7E. 
 
 Fig. 2 - Location of samples of the Aux Vases Formation from Hamilton County. 
 
4 ILLINOIS STATE GEOLOGICAL SURVEY 
 
 summarize the clay minerals found and to define again the mineralogical terms used. 
 
 Five clay mineral groups recognized in the samples are the illite group, the 
 chlorite group, the kaolinite group, the montmorillonite group, and the group com- 
 posed of mixed-layer undifferentiated material. In the illite group two subgroups 
 are recognized: a) well crystallized illite, and b) a poorly ordered, at least partially 
 expandable, subgroup referred to as illite plus mixed-layer material. Similarly, 
 there are two subgroups which comprise the chlorite group: a) a well crystallized 
 group referred to as chlorite, and b) a mixture of chlorite and at least partially ex- 
 pandable material referred to as chlorite plus mixed-layer material. 
 
 The term "all mixed-layer material" as used herein refers to all of the illite 
 plus mixed-layer material, chlorite plus mixed-layer material, montmorillonite, 
 and mixed-layer (undifferentiated) material that is present in a sample, as a single 
 assemblage. 
 
 QUANTITATIVE ESTIMATIONS 
 
 A detailed explanation of the methods used in making quantitative estimates 
 of the clay minerals is presented in Part I of this series. To summarize briefly, 
 two methods were used. 
 
 1) The shales, which are dominantly composed of well ordered illite and 
 chlorite, were estimated quantitatively using the system outlined by Johns et al. 
 (1954). This system is based on a comparison of the first-order peak-area inten- 
 sities of the clay minerals present. 
 
 2) The method used in samples containing a dominant amount of mixed-layer 
 material was one based on a system suggested by Bradley (personal communication, 
 1958). This system is based on the intensities of first-order peaks of illite, chlor- 
 ite, glycol-expanded montmorillonite, and the third-order peak of kaolinite. The 
 intensities of each of these peaks were essentially compared to the comparable 
 peak intensities of "pure" samples of each of these minerals. This method permit- 
 ted more accurate estimates of the relative abundance of the poorly ordered com- 
 ponents than could be made using the method outlined by Johns et al. (1954) al- 
 though the Johns et al. method gave the best results in samples dominated by well 
 ordered clay minerals. 
 
 As the Aux Vases samples from Hamilton County are restricted to a small 
 area and to a small stratigraphic zone, it was assumed that the sediments were 
 derived from the same source area and were deposited at about the same time and 
 under essentially the same environmental conditions. Therefore, it was supposed 
 that quantitative variations could be shown by comparing the intensities of the 
 first-order peaks of the various clay minerals. This was done by comparing the 
 areas (as measured above the projected background intensity) comprising the peaks 
 of the various clay minerals. The quantitative estimates were derived using this 
 method. 
 
 DISTRIBUTION OF CLAY MINERALS 
 
 The investigation of many subsurface samples of sandstones and shales of 
 Chester age has led to some general conclusions pertaining to characteristic clay 
 mineral suites which appear in the different lithologies. 
 
 The shales, even those intimately associated with sandstones, are character- 
 istically composed dominantly of illite and chlorite with rarely more than a few 
 parts in ten of illite plus mixed-layer material and of chlorite plus mixed-layer 
 material. Kaolinite and montmorillonite are rarely present. 
 
CLAY MINERAL VARIATIONS 
 
 The clay minerals in the sandstones are mainly illite plus mixed-layer 
 material and kaolinite. Chlorite plus mixed-layer material and illite are commonly 
 present in lesser proportions, and montmorillonite is occasionally present in minor 
 amounts. 
 
 Intermediate porous rocks typically exhibit clay mineral compositions grada- 
 tional between the above two described suites. 
 
 The study of these Chester samples also suggests that there is a significant 
 difference between the clay mineral compositions of oil-bearing and non-oil-bearing 
 sandstones. Table 1 presents the clay mineral compositions of 46 core samples of 
 Chester sandstones and shales from the deep part of the Illinois Basin. By compar- 
 ing the clay mineral compositions of the shales with those of the oil-bearing and 
 non-oil-bearing sandstones of each formation (in formations where such comparisons 
 can be made), it can be seen that the differences most readily apparent are changes 
 in the proportionate amounts of illite, kaolinite, and all mixed-layer material 
 (especially illite plus mixed-layer material). However, the average compositions 
 of the three types of samples is more strikingly exhibited by comparing the average 
 compositions of each type (shown at the bottom of the table). 
 
 The differences between the shales and the two types of sandstones (when 
 combined) is striking (Part I). It has been recognized that post-lithification altera- 
 tion of clay minerals occurs in permeable sediments, not only in outcrop exposures 
 but also in the subsurface. However, there is also a noticeable difference between 
 oil-bearing and non-oil-bearing sandstones that were deposited under approximately 
 the same conditions in a relatively restricted area (the deep part of the Illinois 
 Basin) . 
 
 A A Oil-bearing sandstone 
 
 l ~ l n Non-oil-bearing sandstone 
 
 Fig. 3 - Average of clay mineral composition of Chester shales, oil-bearing 
 sandstones, and non-oil-bearing sandstones. 
 
 The differences in clay mineralogy between the oil-bearing and non-oil- 
 bearing sandstones, as shown in table 1 and figure 3, are essentially the differences 
 in the relative amounts of the well crystallized three-layer clay minerals present 
 in each. The oil-bearing sandstones generally are composed of only two parts in 
 ten illite and chlorite. The non-oil-bearing sandstones exhibit usually more than 
 twice that amount. Conversely, the oil-bearing sandstones exhibit approximately 
 twice as much all mixed-layer material as do the non-oil-bearing sandstones. 
 Generally, the proportion of kaolinite in the oil-bearing sandstones is significantly 
 greater than that in the non-oil-bearing sandstones. 
 
ILLINOIS STATE GEOLOGICAL SURVEY 
 
 Table 1. - Clay Mineral Composition of Chester Shales, 
 
 Formation 
 
 
 
 
 
 and sample 
 
 County 
 
 Illite 
 
 Chlorite 
 
 Kaolinite 
 
 
 
 Degonia 
 
 
 
 4D 
 
 White 
 
 2 
 
 5 
 
 Tr 
 
 1987D 
 
 White 
 
 1 
 
 2 
 
 2 
 
 309 
 
 Gallatin 
 
 8 
 
 - 
 
 1.5 
 
 1953D 
 
 Posey (Ind.) 
 
 4.5 
 Palestine 
 
 4 
 
 .5 
 
 2090 
 
 White 
 
 1.5 
 
 1.5 
 
 4.5 
 
 1032A 
 
 Williamson 
 
 - 
 
 - 
 
 2.5 
 
 487 
 
 Saline 
 
 1.5 
 
 2 
 
 4+ 
 
 133E 
 
 Williamson 
 
 1 
 
 5.5 
 
 1.5 
 
 1032B 
 
 Williamson 
 
 2 
 Waltersburg 
 
 5.5 
 
 1 + 
 
 CS1 
 
 White 
 
 .5 
 
 4 
 
 2.5 
 
 1716 
 
 Posey (Ind.) 
 
 1 
 
 4 
 
 Tr 
 
 1692 
 
 Edwards 
 
 1 
 
 3 
 
 3 
 
 133F 
 
 Williamson 
 
 1 
 
 5 
 
 1 
 
 308 
 
 Wabash 
 
 4 
 Tar Springs 
 
 3 
 
 2 
 
 1427 
 
 Franklin 
 
 1 
 
 1 
 
 5 
 
 2191 
 
 White 
 
 1 
 
 2 
 
 2 
 
 1840 
 
 White 
 
 - 
 
 1 
 
 4 
 
 1427B 
 
 Franklin 
 
 - 
 
 - 
 
 7 
 
 5 38 
 
 Hamilton 
 
 ? 
 
 ? 
 
 Med. 
 
 1000 
 
 Saline 
 
 1.5 
 
 1.5 
 
 5 
 
 1853A 
 
 Gallatin 
 
 3 
 Cypress 
 
 Tr 
 
 3 
 
 501 
 
 Perry 
 
 1 
 
 2.5 
 
 2 
 
 1073 
 
 Clinton 
 
 2 
 
 2 
 
 1.5 
 
 397 
 
 Crawford 
 
 1 
 
 Tr 
 
 5 
 
 1201 
 
 Edwards 
 
 2 
 
 3.5 
 
 1.5 
 
 133.1 
 
 White 
 
 1 
 Paint Creek 
 
 2 
 
 4 
 
 432 
 
 Hamilton 
 
 .5 
 
 2.5 
 
 - 
 
 1339 
 
 White 
 
 1.5 
 
 3 
 
 4.5 
 
 2578PC 
 
 Hardin 
 
 8 
 
 - 
 
 - 
 
 1618 
 
 Fayette 
 
 4.5 
 
 Tr 
 
 - 
 
CLAY MINERAL VARIATIONS 
 
 Oil-Bearing Sandstones, and Non-Oil-Bearing Sandstones 
 
 Ulite plus Chlorite plus Mixed-layer 
 
 mixed-layer mixed-layer material 
 
 material material Montmorillonite (undifferentiated) 
 
 Lithology : 
 
 1 
 
 1.5 
 Tr 
 .5 
 
 .5 
 .5+ 
 
 .5 
 
 Tr 
 Tr 
 
 1 
 
 1 
 
 3.5 
 Tr 
 .5 
 
 1 
 
 1.5+ 
 
 Tr 
 Tr 
 
 Tr 
 .5 
 
 Degonia 
 
 Tr? 
 Tr 
 
 Tr? 
 
 Palestine 
 
 Tr? 
 Waltersburg 
 Tr? 
 ? 
 
 Tar Springs 
 
 .5 
 
 2 
 
 - 
 
 2 
 
 3 
 
 - 
 
 1.5 
 
 1.5 
 
 _ 
 
 Weak 
 
 Weak 
 
 ? 
 
 1 
 
 1 
 
 - 
 
 4 
 
 
 Cypress 
 
 2 
 
 2 
 
 Tr 
 
 1.5 
 
 2.5+ 
 
 Tr? 
 
 2 
 
 2 
 
 - 
 
 2 
 
 Tr 
 
 Tr 
 
 2 
 
 1 
 
 Paint Creek 
 
 1 
 
 .5 
 
 - 
 
 Tr 
 
 Tr 
 
 - 
 
 .5 
 
 - 
 
 1.5? 
 
 4.5 
 
 - 
 
 - 
 
 Tr 
 
 7.5 
 
 4.5 
 
 2 
 
 2 
 
 .5 
 5 
 Weak 
 
 N-o-b ss 
 O-b ss 
 Shale 
 Shale 
 
 O-b ss 
 O-b ss 
 N-o-b ss 
 N-o-b ss 
 Shale 
 
 O-b ss 
 
 Slightly O-b ss 
 N-o-b ss 
 Shale 
 Shale 
 
 O-b ss 
 
 O-b ss 
 
 O-b ss 
 
 O-b ss 
 
 O-b ss 
 
 Argillaceous ss 
 
 N-o-b ss 
 
 O-b ss 
 O-b ss 
 O-b ss 
 N-o-b ss 
 N-o-b ss 
 
 O-b ss 
 N-o-b ss 
 Shale (mud) 
 Shale 
 
 O-b ss = Oil-bearing sandstone; N-o-b ss = Non-oil-bearing sandstone. 
 
ILLINOIS STATE GEOLOGICAL SURVEY 
 
 Table 1. - 
 
 Formation 
 
 
 
 
 
 and sample 
 
 County 
 
 Illite 
 
 Chlorite 
 
 Kaolinite 
 
 
 
 Bethel 
 
 
 
 2396 
 
 Wabash 
 
 - 
 
 2 
 
 3 
 
 2392 
 
 Clay 
 
 .5 
 
 3 
 
 4 
 
 1343 
 
 Jackson 
 
 Med. 
 
 Weak 
 
 Weak 
 
 2605 
 
 Bond 
 
 .5 
 
 2 
 
 2.5 
 
 133.2 
 
 White 
 
 1.5 
 
 5.5 
 
 2 
 
 2507 
 
 White 
 
 3.5 
 
 6 
 
 - 
 
 2634 
 
 Fayette 
 
 1.5 
 Renault 
 
 7 
 
 Tr 
 
 2365 
 
 Franklin 
 
 8.5 
 
 - 
 
 - 
 
 2750 
 
 Hamilton 
 
 4.5 
 Aux Vases 
 
 5.5 
 
 
 136.1 
 
 Hamilton 
 
 4 
 
 4 
 
 1 
 
 2634 
 
 Fayette 
 
 2+ 
 
 4.5 
 
 2+ 
 
 1987 
 
 White 
 
 1.5 
 
 4 
 
 2- 
 
 2789 
 
 White 
 
 2.5 
 
 4+ 
 
 1 
 
 2798 
 
 Saline 
 
 5.5 
 
 4 
 
 - 
 
 3231 
 
 Clay 
 
 5+ 
 
 4 
 
 - 
 
 2336 
 
 Johnson 
 
 8 
 Averages 
 
 1 
 
 
 Oil-bearing 
 
 sandstone 
 
 .7 
 
 1.6 
 
 3.2 
 
 Non-oil-bea 
 
 ring sandstone 
 
 1.7 
 
 2.7 
 
 2.5 
 
 Shales 
 
 
 4.3 
 
 3.6 
 
 .7 
 
 As the samples discussed above are from various facies and formations, the 
 differences between the oil-bearing and non-oil-bearing sandstones may be a function 
 of availability of samples, of differences in source areas or environments of depo- 
 sition, or of other variables which had little or nothing to do with the presence or 
 absence of oil. A very detailed study of samples from the Thackeray Pool and parts 
 of the Dale and Bungay Consolidated Pools representing a limited period of depo- 
 sition over a small area in which the sediments were probably derived from essen- 
 tially the same source areas and deposited under essentially the same environments 
 of deposition should reduce these variables to a minimum. Thus, differences be- 
 tween oil-bearing and non-oil-bearing sandstones would strongly favor a connec- 
 tion with the presence or absence of oil. 
 
 Table 2 represents the clay mineral compositions of the 26 samples which 
 are from Thackeray Pool and portions of the Bungay and Dale Consolidated Pools. 
 Table 2 differs from table 1 in that the small proportions of montmorillonite found 
 in the samples have been included in the proportion of mixed-layer (undifferentiated) 
 
Continued, 
 
 CLAY MINERAL VARIATIONS 
 
 Illite plus 
 
 Chlorite plus 
 
 
 Mixed layer 
 
 
 mixed-layer 
 
 mixed-layer 
 
 
 material 
 
 
 material 
 
 material 
 
 Montmorillonite 
 
 (undifferentiated) 
 
 Lithology 
 
 3 
 
 2 
 
 1 
 
 1 
 
 Weak 
 
 Weak 
 
 2.5 
 
 2.5 
 
 Bethel 
 
 Tr 
 
 O-b ss 
 O-b ss 
 N-o-b ss 
 N-o-b ss 
 Shale 
 Shale 
 Shale 
 
 Renault 
 
 Tr 
 
 2.5+ 
 
 Tr 
 
 Tr 
 
 1 
 
 .5 
 
 Tr 
 
 .5 
 
 . 
 
 _ 
 
 Tr 
 
 - 
 
 Tr 
 
 Aux Vases 
 
 
 Tr 
 
 Tr 
 
 - 
 
 1 
 
 Tr 
 
 1 
 
 Tr 
 
 Shale 
 Shale 
 
 Shale 
 Shale 
 Shale 
 Shale 
 Shale 
 Shale 
 Shale 
 
 1.2 
 
 1.6 
 
 1.3 
 
 .7 
 
 .8 
 
 .2 
 
 Averages 
 
 
 .1 
 
 1.3 
 
 - 
 
 .5 
 
 .1 
 
 .3 
 
 material. The presence of distinct montmorillonite was noted only in sample 2315, 
 but possible trace occurrences were noted in samples 1581 and 1765, and therefore 
 it is included as an undifferentiated mixed-layer component. No kaolinite was 
 found in any of these samples, therefore kaolinite was deleted from table 2. W. A. 
 White and W. E. Parham (personal communication, 1959) have convincing evidence, 
 based on studies of the Pennsylvanian sediments of the Illinois Basin, that kaolinite 
 is generally restricted to near-shore environments. Smoot (1959a) has also presented 
 evidence of this for the pre-Mississippian rocks of the Illinois Basin. Therefore, 
 it may be concluded that the absence of kaolinite in the Hamilton County Aux Vases 
 samples indicates that the samples were deposited in an off-shore environment. 
 
 Tables 1 and 2 exhibit similar differences among the clay mineral compo- 
 sitions of the shales, the oil-bearing sandstones, and the non-oil-bearing sand- 
 stones. It is apparent from the samples that in this limited area, the two sandstone 
 types represented are more nearly alike in composition than are the samples discussed 
 
10 ILLINOIS STATE GEOLOGICAL SURVEY 
 
 Table 2. - Clay Mineral Compositions of Aux 
 
 Sample (see fig. 2) Illite Chlorite 
 
 Bungay Consolidated Pool 
 
 1631A 1+ 1 
 
 1779 2+ 2+ 
 
 1784 5+ .5 
 
 356 3.5 Tr 
 
 1631B 4+ 1+ 
 
 461 4+ 2 
 
 936 6.5 
 
 1529 5 .5 
 
 Dale Consolidated Pool 
 
 2399 1 Tr 
 
 620 1 1 
 
 730 1+ 1 
 
 1755A 6 Tr 
 
 1941A 1 Tr 
 
 1941B 6 1.5 
 
 2315A 3.5 1.5+ 
 
 1755B 6 1 
 
 2315B 7- Tr 
 
 Thackeray Pool 
 
 1545 2+ 2 
 
 1601 5.5 Tr 
 
 1694 2.5 1.5 
 
 1935 2- 1.5+ 
 
 1581A 2.5 1.5 
 
 1934A 5.5 1+ 
 
 1581B 6.5 Tr 
 
 1934B 7 Tr 
 
 1765 7 Tr 
 
 Average 
 
 Oil-bearing sandstones 2.4 1.1 
 
 Non-oil-bearing sandstones 4.4 1.1 
 
 Shales 6.5 .5 
 
CLAY MINERAL VARIATIONS 
 
 11 
 
 Vases Sandstones and Shales in Hamilton County 
 
 Illite plus 
 
 Chlorite pli 
 
 JS 
 
 
 Mixed-layer 
 
 
 mixed-layer 
 
 mixed-laye 
 
 r 
 
 
 material 
 
 
 material 
 
 material 
 
 
 
 (undifferentiated) 
 
 Lithology* 
 
 
 
 Bunqay 
 
 Consolidated Pool 
 
 
 1.5+ 
 
 1+ 
 
 
 
 
 4.5 
 
 O-b ss 
 
 1.5 
 
 1 
 
 
 
 
 3+ 
 
 O-b ss 
 
 2+ 
 
 Tr 
 
 
 
 
 2 
 
 O-b mica ss 
 
 3+ 
 
 1- 
 
 
 
 
 2 
 
 N-o-b ss 
 
 2.5 
 
 Tr 
 
 
 
 
 1.5 
 
 N-o-b argil ss 
 
 2 
 
 Tr 
 
 
 
 
 1+ 
 
 N-o-b ss 
 
 1 
 
 1.5 
 
 
 
 
 1 
 
 Shale 
 
 3 
 
 Tr 
 
 
 
 
 1+ 
 
 Shale 
 
 
 
 Dale Consolidated Pool 
 
 
 2 
 
 1+ 
 
 
 
 
 5.5 
 
 O-b ss 
 
 2 
 
 1 
 
 
 
 
 5 
 
 O-b ss 
 
 3- 
 
 1 
 
 
 
 
 4- 
 
 O-b ss 
 
 2+ 
 
 Tr 
 
 
 
 
 1 
 
 N-o-b mica ss 
 
 4 
 
 1 
 
 
 
 
 4+ 
 
 N-o-b ss 
 
 1.5 
 
 Tr 
 
 
 
 
 Tr 
 
 N-o-b mica ss 
 
 1.5+ 
 
 1 
 
 
 
 
 1+ 
 
 N-o-b ss 
 
 2 
 
 Tr 
 
 
 
 
 1 
 
 Shale 
 
 2- 
 
 Tr 
 
 
 
 
 1- 
 
 Shale 
 
 
 
 Thackeray 
 
 Pool 
 
 
 
 2.5 
 
 - 
 
 
 
 
 3+ 
 
 O-b ss 
 
 2 
 
 Tr 
 
 
 
 
 1.5 
 
 O-b argil ss 
 
 3.5 
 
 1 
 
 
 
 
 1.5 
 
 O-b ss 
 
 2+ 
 
 1- 
 
 
 
 
 3.5 
 
 O-b ss 
 
 2.5 
 
 1 
 
 
 
 
 2.5 
 
 N-o-b ss 
 
 1+ 
 
 - 
 
 
 
 
 2 
 
 N-o-b ss 
 
 1 
 
 Tr 
 
 
 
 
 1+ 
 
 Shale 
 
 1+ 
 
 Tr 
 
 
 
 
 Tr 
 
 Shale 
 
 1+ 
 
 Tr 
 
 
 
 
 1 
 
 Shale 
 
 
 
 
 Average 
 
 
 
 2.2 
 
 .8 
 
 
 
 
 3.4 
 
 
 2.3 
 
 .5 
 
 
 
 
 1.8 
 
 
 1.6 
 
 .4 
 
 
 
 
 .9 
 
 
 * O-b ss = Oil-bearing sandstone 
 
 N-o-b ss = Non-oil-bearing sandstone 
 
 Mica = micaceous 
 Argil = argillaceous 
 
12 
 
 ILLINOIS STATE GEOLOGICAL SURVEY 
 
 above from a much larger area. The average Hamilton County sandstone sample 
 has approximately the same proportions of chlorite, illite plus mixed-layer material, 
 and chlorite plus mixed-layer material. The most noticeable differences are in the 
 illite and the mixed-layer (undifferentiated) material proportions. The non-oil-bear- 
 ing sandstones have approximately twice the proportion of illite as the oil-bearing 
 samples; the oil-bearing sandstones have approximately twice the proportion of 
 mixed-layer (undifferentiated) material as those without oil. These differences are 
 also demonstrated graphically in figure 4 which represents the average clay mineral 
 compositions of the shales, oil-bearing sandstones, and non-oil-bearing sandstones, 
 The most striking differences are between the proportions of illite and all mixed- 
 layer materials. 
 
 , Oil-beormg sandstone 
 I Non-oil-bearing sandstone 
 Shale 
 
 Fig. 4 - Average clay mineral composition of shales, oil-bearing sandstones, and 
 non-oil-bearing sandstones of the Aux Vases Formation from Hamilton County. 
 
 DISCUSSION 
 
 On the basis of the clay mineral analyses presented here, it seems apparent 
 that the differences between clay mineral compositions of oil-bearing and of non- 
 oil-bearing sandstones are due, at least in part, to the presence of oil. These 
 variations are characterized by the proportionate differences in well crystallized 
 three-layer clay minerals. The non-oil-bearing sandstones have appreciably higher 
 proportions of illite and, generally, chlorite; oil-bearing sandstones are proportion- 
 ately higher in kaolinite (if present). 
 
 In many instances, especially among the Hamilton County samples, these 
 differences are apparent in samples of sediments which were probably deposited 
 under the same conditions and derived from the same source areas. It would seem, 
 therefore, that the differences are not inherent, but that they developed during some 
 period after deposition. These observations appear to have some bearing on the 
 mode and time of accumulation of oils. 
 
CLAY MINERAL VARIATIONS 13 
 
 The average clay mineral composition of very near-shore deposits in the 
 Illinois Basin (Smoot 1959b) is similar to that of the oil-bearing sandstones as 
 shown in tables 1 and 2. This may suggest that the clay mineral suites associated 
 with oil accumulations, even though found in off-shore facie s, are more nearly like 
 the clay mineral suites originally introduced into the sedimentary basin than are the 
 non-oil-bearing clay suites. 
 
 Degraded three-layer clay minerals, which would be expected to have been 
 a major portion of the clay mineral suite introduced into the Illinois Basin during 
 Chester time, would have a relatively high crystallite charge. In the sedimentary 
 basin this charge would be satisfied by the interlayer adsorption of cations. If 
 organic cations were available, they would satisfy the cation deficiency of the 
 degraded clays. Ensminger and Gieseking (1942) suggested that certain adsorbed 
 organic compounds can reduce the exchange capacity of clays, which otherwise 
 have high exchange capacities, by blocking the interlayer positions. Montmorillon- 
 itic clay minerals generally have the highest exchange capacities and, therefore, 
 would be prone to adsorb organic compounds that might be available more readily 
 than better crystallized illitic or chloritic clay minerals. If such a situation existed, 
 the clays closely associated with the organic compounds would have been prevented 
 from regeneration, even after burial, whereas the clays not associated with the 
 organic compounds may have become better organized during diagenesis and burial. 
 
 The idea that oil-bearing clays have been closely associated with organic 
 compounds since, essentially, their deposition has merit only if it can be shown 
 that 1) the hydrocarbons were available at the time of or soon after deposition, and 
 2) that the oil accumulations now found with these clays were in place soon after 
 deposition. If these points could be proved, probably it could also be proved that 
 oil accumulations are not the product of migration. Because the non-migration 
 accumulation idea is outweighed by the evidence for accumulation by migration, it 
 must be assumed at present that most oil accumulations are the product of migration 
 after lithification and subsequent structural deformation. 
 
 As discussed in Part I and above (under "Distribution of Clay Minerals"), 
 many investigators have recognized that post-lithification alteration of clay minerals 
 occurs in permeable sediments. Such alterations are generally degradational, 
 brought about by the circulation of fluids, the chemical composition of which changes 
 from time to time. If this is so, it seems logical that the greater the permeability 
 the greater the amount of circulation, the greater the changes in composition, and, 
 therefore, the greater the amount of degradation of the clay minerals. 
 
 If oil migrates mainly by the action of fluid movement after structural shifts 
 of position, it seems reasonable that the oil would migrate along the most permeable 
 paths available and be entrapped in the most permeable positions along the struc- 
 tures. Hence, this would be a reason for the differences of clay minerals between 
 oil-bearing and associated non-oil-bearing sandstones. This idea is further 
 strengthened by the fact that, at some places, non-oil-bearing permeable sand- 
 stones have clay mineral suites very similar to those of oil-bearing sandstones 
 (for example, compare samples 2090, 487, and 501, table 1, and 1941A, 1545, and 
 1581A, table 2). This suggests that possibly the same amounts of post-lithification 
 degradation occurred but that, in some instances, the degrading fluids did not supply 
 oil to the clays at a later time. 
 
 A comparison between the clay mineral suites in the oil-bearing and non-oil- 
 bearing sandstones, especially in the Hamilton County Aux Vases samples, sug- 
 gests that some of the clays may have been at least partly degraded between the 
 
ILLINOIS STATE GEOLOGICAL SURVEY 14 
 
 time of lithification and the time of oil accumulation. The strong affinity of mont- 
 morillonite for organic compounds is known (Cowan and White, 1958) and so it 
 seems logical to suppose that the clay mineral mixtures common in oil-bearing 
 sandstones and having montmorillonite as a common component would have essen- 
 tially this same strong affinity. Thus, it seems unlikely that once the exchange 
 positions on these mixtures were satisfied by hydrocarbons, they would again be 
 replaced. Therefore, after oil-accumulation, it seems improbable that further degra- 
 dation could take place. 
 
 If the reasoning is valid, it follows that if degradation of clay minerals took 
 place it must have happened before the oil accumulated. This suggests that oil 
 accumulation occurs after lithification. If formation-fluid circulation is brought 
 about by structural readjustments, this suggests that oil accumulation may occur 
 after structural adjustment and after a certain amount of non-oil-bearing, degrading 
 fluid had passed through the reservoir. If a fairly constant rate of movement (circu- 
 lation) can be assumed, then time is directly proportional to distance. Thus, it is 
 suggested that in some instances oil may have migrated over relatively long dis- 
 tances. Conversely, if the clay mineral suites are very degraded, oil-bearing 
 reservoirs exhibiting clay mineral suites composed of comparatively well crystal- 
 lized clay minerals may have obtained oil from nearby source sediments. 
 
 REFERENCES 
 
 Cowan, C. T., and White, D., 1958, The mechanism of exchange reactions be- 
 tween sodium-montmorillonite and various n-primary aliphatic amine salts: 
 Faraday Soc. Trans., v. 54, pt. 5, no. 425, May, p. 691-698. 
 
 Ensminger, L. E., and Gieseking, J. E., 1942, Resistance of clay-adsorbed pro- 
 teins to proteolytic hydrolysis: Soil Science, v. 53, p. 205-209. 
 
 Johns, W. D., Grim, R. E., and Bradley, W. F., 1954, Quantitative estimations 
 
 of clay minerals by diffraction methods: Jour. Sed. Petrology, v. 24, no. 4, 
 p. 242-251. 
 
 Narain, Kedar, 1959, A study of clay minerals from certain producing and nonpro- 
 ducing oil sands of Hamilton County, Illinois: Masters thesis, University 
 of Illinois, Urbana, Illinois. 
 
 Smoot, T. W., 1959a, Clay mineralogy of pre-Pennsylvanian sandstones and shales 
 of the Illinois Basin: Doctoral thesis, University of Illinois, Urbana, 
 Illinois. 
 
 Smoot, T. W., 1959b, Clay mineralogy as applied to secondary recovery problems: 
 Producers Monthly, v. XXIII, no. 8, June, p. 32-36. 
 
 Smoot, T. W., 1959c, Clay mineralogy of pre-Pennsylvanian sandstones and shales 
 of the Illinois Basin, Part I. — Relation of permeability to the clay mineral 
 suites: Illinois Geol. Survey Circ. 286. 
 
 Illinois State Geological Survey Circular 287 
 14 p., 4 figs., 2 tables, 1960 
 
xmrnzii 
 
 CIRCULAR 287 
 
 ILLINOIS STATE GEOLOGICAL SURVEY 
 
 URBANA