Albany Shale Group Research Articles

Formation waters from Mississippian-Pennsylvanian reservoirs, Illinois basin, USA: Chemical and isotopic constraints on evolution and migration

We have analyzed a suite of seventy-four formation-water samples from Mississippian and Pennsylvanian carbonate and siliciclastic strata in the Illinois basin for major, minor, and trace element concentrations and for strontium isotopic composition. A subset of these samples was also analyzed for boron isotopic composition. Data are used to interpret origin of salinity and chemical and Sr isotopic evolution of the brines and in comparison with a similar data set from an earlier study of basin formation waters from Silurian-Devonian reservoirs. Systematics of Cl-Br-Na show that present Mississippian-Pennsylvanian brine salinity can be explained by a combination of subaerial seawater evaporation short of halite saturation and subsurface dissolution of halite from an evaporite zone in the middle Mississippian St. Louis Limestone, along with extensive dilution by mixing with meteoric waters. Additional diagenetic modifications in the subsurface interpreted from cation/Br ratios include K depletion through interaction with clay minerals, Ca enrichment, and Mg depletion by dolomitization, and Sr enrichment through CaCO 3 recrystallization and dolomitization. Ste. Genevieve Limestone (middle Mississippian) formation waters show 87Sr 86Sr ratios in the range 0.70782–0.70900, whereas waters from the siliciclastic reservoirs are in the range 0.70900–0.71052. Inverse correlations between 87Sr 86Sr and B, Li, and Mg concentrations suggest that the brines acquired radiogenic 87Sr through interaction with siliciclastic minerals. Completely unsystematic relations between 87Sr 86Sr and 1/Sr are observed; Sr concentrations in Ste. Genevieve and Aux Vases (middle Mississippian) waters appear to be buffered by equilibrium with respect to SrSO 4. Although there are many similarities in their origin and evolution, these formation waters are distinguished from Silurian-Devonian brines in the basin by elevated Cl Br and Na Br ratios and by unsystematic Sr isotope relationships. Thus waters from these two major segments of the Illinois basin stratigraphic column form distinct geochemical regimes which are separated by the New Albany Shale Group (Devonian-Mississippian) regional aquitard. Geochemical evolution appears to have been influenced significantly by Paleozoic and Mesozoic hydrologic flow systems in the basin.

Br-Cl-Na systematics in Illinois basin fluids: Constraints on fluid origin and evolution

The authors present here bromide, chloride, and sodium data for fluids from reservoirs of Ordovician through Pennsylvania age in the Illinois basic which suggest that remnant marine fluids contribute significantly to fluid Cl budgets. Cl/Br and NaBr ratios for Ordovician through Devonian formation fluids are relatively uniform and near those for seawater, despite greater than a factor of ten range in Cl concentration. In contrast, fluids from Mississippian and Pennsylvanian reservoirs, separated from older reservoirs by the New Albany Shale Group, have more variable fluid Cl/Br and Na/Br ratios, most of which are significantly greater then those of seawater. The 1:1 stoichiometry of Cl and Na increases for Mississippian and Pennsylvanian formation fluids is consistent with halite dissolution. Nevertheless, Br systematics and mass-balance considerations indicate that he overall Cl budget of Illinois basin formation fluids appears to be more significantly influenced by the contribution from subaerially evaporated seawater than by halite dissolution.

Pulsed laser fluorescence microscopy of coal macerals and dispersed organic material

A new pulsed laser microscopy technique was applied to the study of fluorescence from liptinite macerals in the time and wavelength domains. Useful parameters for coal characterization are the fluorescence decay times and percentage contributions of the individual fluorescing compounds to the total intensity. Characteristic decay times in the nanosecond and sub-nanosecond range are obtained for sporinite, fluorinite, cutinite and resinite of the Lower Kittanning coal seam and alginite of the New Albany shale group of the Illinois Basin. Time-resolved emission spectra for the individual fluorophores are obtained and generally found to be broad but specific for each maceral type. The total sporinite fluorescence comes from fluorophores whose individual spectra peak in the blue-green and yellow regions. The percentage contributions from each fluorophore vary systematically with increasing coal rank. The previously observed red-shift in the conventional composite spectra is interpreted, especially for sporinite. The new laser microscopy is described in some detail. The reliability of the method was tested with mixtures of selected organic compounds in solution and subsequent analysis. The fluorescence decay times and time-resolved spectra agree with those for the pure substances under certain conditions. These conditions apply to the coal macerais studied. Generally, one-, two- and three-component mixtures can be resolved if the component lifetimes differ by a factor of two or more and the individual contributions to the total intensity exceed 10%. Fluorescence decay times of 200 ps and greater can be measured with an accuracy of about 100 ps.

Organic geochemical characterization of the New Albany Shale group in the Illinois Basin

Benzene extractable aliphatic hydrocarbons from the New Albany Shale in the Illinois Basin were characterized by gas chromatography and mass spectrometry, and the total organic matter of the shale was characterized by solid state carbon-13 cross polarization magic angle spinning nuclear magnetic resonance. Core samples from a northwest-trending cross-section of the Illinois Basin were studied. Gas chromatography (GC) and gas chromatography-mass spectrometric analysis (GC/MS) data indicate a regional variation of the aliphatic composition of the shale extracts. A positive, linear relationship between the two ratios, pristane/ n-C 17 and phytane/ n-C 18, is indicated. The NMR results indicated that organic matter deposited in northwestern Illinois shale is relatively high in aliphatic hydrocarbon content while, in contrast, organic matter found in southeastern Illinois shale is relatively low in aliphatic hydrocarbon content. Our findings suggest that the organic variation of the shale is mainly due to the differences in thermal maturity of the shale organic matter and the use of pristane/ n-C 17 ratio as a thermal parameter in the study of oil may be extended to the study of the ancient sediments.

Petrographic, Geochemical, and Paleohydrologic Evidence of Nature of Petroleum Migration in Illinois Basin: ABSTRACT

Detailed studies of the petrography and geochemistry of petroleum source rocks, the geochemistry of petroleum accumulations, and the paleohydrology of the Illinois basin suggest an episode of long-range migration of Devonian-sourced petroleum during a period of regional groundwater flow. Petrographic analyses of samples of the New Albany Shale group (Devonian/Mississippian) were used to define lateral and vertical variation in composition and thermal maturity of organic matter within the basin. These data delineate likely New Albany Shale group petroleum source areas. GC, GCMS, and carbon isotopic analyses of thermally mature New Albany Shale in southeastern Illinois and Silurian-reservoired petroleum samples from central Illinois were used in making oil-oil and oil-source rock correlations. These correlations indicate long-range lateral and downward cross-stratigraphic net migration. Compaction-driven and elevation head-driven ground-water flows within the basin were numerically modeled using available stratigraphic, structural, and hydrologic data. Calculations based on compaction-driven flow show the possibility of down-stratigraphic migration. Compaction-driven flow, however, cannot explain the amount of lateral transport inferred. Regional ground-water flow due to the uplift of the Pascola arch could explain the long-range lateral migration. Calculations of the effects of advective heat transport by elevation head-driven flow agree with estimates of temperatures made from fluid inclusions in basin mineralization. End_of_Article - Last_Page 454------------

Natural Gas Potential of the New Albany Shale Group (Devonian-Mississippian) in Southeastern Illinois

Abstract Data from geologic and geochemical studies of the New Albany shale group indicate that a 19-county area of southeastern Illinois is a favorable area to explore for gas in Devonian shale. Although gas shows in the shales have been encountered in several wells drilled in this area, no attempts were made to complete or evaluate a shale gas well until 1979. In 1979, core samples from two Wayne County wells were obtained, permitting the first quantitative assessment of gas content of the shales in this area. Seventy core samples from the two wells were sealed in airtight canisters at the drilling site for off-gas analysis. The quantities of shale gas released from the core samples in a 34-day period ranged from 0.16 to 2.40 cu ft HC/cu ft (0.16 to 2.40 m3 HC/m3)* of shale. This gas is richer in heavy hydrocarbons than is the average "pipeline gas." It has a calculated average BTU value of 1,240 Btu/cu ft (46 200 kJ/m3). Because the proportion of nonhydro-carbon gases is unknown, the calorific content of produced gas would necessarily be slightly lower. The gas-bearing intervals generally correspond with high radioactivity intervals on gamma-ray logs. The quantities of shale gas in core samples from these wells are similar to those in gas-producing areas of Devonian shale in the Appalachian basin. However, because the New Albany shale is much thinner than its Appalachian basin equivalents, the total gas resource is probably much smaller. Conventional rotary drilling with mud base drilling fluids likely causes extensive formation damage and may account for the paucity of gas shows and completion attempts in the Devonian shales; therefore, commercial production of shale gas in Illinois probably will require novel drilling and completion techniques not commonly used by local operators.

Correlation of natural gas content to iron species in the New Albany shale group

Mössbauer parameters were obtained for four Illinois Basin shales and their corresponding < 2μm clay fractions from wells drilled through the New Albany Shale Group in Henderson, Tazewell, and Effingham counties in Illinois and Christian County in Kentucky. Off-gas analysis indicated that the Illinois cores were in an area of low gas potential, while the Kentucky core was in an area of moderate-to-good potential. Iron-rich dolomite (ankerite) was found in the Kentucky core but not in the Illinois cores. In the Kentucky core, gas content could be correlated with the ankerite in the bulk sample, the Mössbauer M (2) species in the clay fraction, and a ferrous iron species in the clay fraction. The location of the greatest concentration of natural gas in the Kentucky core could be predicted by following the changes in percentage concentration of these iron species when plotted against the depth of burial of the core sample.

Paleoenvironment of the New Albany Shale Group (Devonian-Mississippian) of Illinois

ABSTRACT The distribution of lithofacies in the New Albany Shale Group of Illinois was determined by wave energy, bottom oxygenation, and bottom topography in a deep water stratified anoxic basin. A transect from the margin to the center of the Illinois Basin reveals a complete transition from high energy, aerobic, shallow-water environments to quiet, anaerobic, deep-water environments. Shallow areas at the margin of the basin are characterized by rapid facies transitions over short distances. High energy, very shallow conditions are recorded by oolitic-skeletal grainstones and packstones with abundant brachiopods, crinoids, trilobites, and other calcified marine invertebrates. Bioturbation did not destroy primary sedimentary structures in these facies. Offshore, less agitated areas are represented by highly bioturbated carbonate wackestones, argillaceous quartz siltstones, and greenish-gray mudstones. Calcified invertebrates are generally rare in these facies, indicating deposition in dysaerobic conditions. Basinward, slope areas are characterized by olive-gray to black, weakly bioturbated shales commonly interbedded with thickly laminated black shales. Trace fossil , including Zoophycos, Chondrites, and Planolites, are abundant along the bases of the olive-gray beds. In areas where the anaerobic/dysaerobic boundary intersected the bottom slope, slight fluctuations of the position of the boundary resulted in thin interbedding of olive-gray and black shales and laterally persistent interfingering of the two lithologies. Anaerobic conditions prevailed during most of New Albany time in the deepest areas of the basin, and finely laminated, undisturbed, pelagic black shales were deposited.

Relation of Depositional Facies and History to Hydrocarbon Generation in New Albany Shale Group (Devonian-Mississippian) of Illinois: ABSTRACT

End_Page 692------------------------------The distribution of potential hydrocarbon source beds within the New Albany Shale group of Illinois was determined by studies of the stratigraphy, lithology, and organic matter of the shales. Shelf-to-basin correlations (across western Illinois to southern Illinois and western Kentucky) reveal a complete and continuous transition from high-energy, aerobic, shallow-water ( 150 m ?) environments (finely laminated black shales). The types and abundance of the organic matter preserved within the shales were predominantly controlled by the depositional environment. Appreciable amounts (3 to 15%) of mixed humic-sapropelic kerogen were preserved in the anaerobic black shale environments. The kerogen assemblage is interpreted to be well-preserved, locally derived organic material. Only small quantities (typically <1%) of humic (degraded ?) kerogen were preserved in the dysaerobic greenish-gray shale environments. This kerogen assemblage is interpreted to result from selective preservation of only the organic constituents most resistant to destruction by benthic invertebrates (detritus feeders) and aerobic bacteria. Petroleum generation in the New Albany shales is likely to have occurred only in the aerobic black shales where the sapropelic and liptinite fractions have been preserved and where sufficient organic maturation has taken place. Gas generation may have occurred in the greenish-gray shales where humic kerogen has been preserved selectively, but in very small quantities due to the low maturity and paucity of organic matter in these shales. End_of_Article - Last_Page 693------------

Petrology and Maturation of Dispersed Organic Matter in New Albany Shale Group of Illinois Basin: ABSTRACT

The New Albany Shale group of the Illinois basin is being studied to evaluate its potential for yielding hydrocarbons. As part of this study, coal petrographic techniques have been employed to evaluate the composition and thermal maturity of dispersed organic matter in the shales. Vitrinite reflectance was measured on acid-macerated kerogen separates from 11 cores and 126 cuttings from drill holes through the New Albany Shale in Illinois, Indiana, and western Kentucky. No significant variations in reflectance values were observed within the New Albany at any single location with respect to either depositional facies or depth. An isoreflectance map prepared from the data shows large areas of the Illinois basin where reflectance is uniformly low (> 0.5% Roil) and the organic matter has not yet reached the stage of petroleum generation. Several areas of higher reflectance also are present: (1) near the northern erosional truncation of the New Albany in central Illinois; (2) in east-central Illinois, an area associated with a broad southward-plunging yncline just west of the La Salle anticlinal belt; (3) in Wayne and Hamilton Counties, Illinois, the present area of maximum burial depth; and (4) in extreme southeastern Illinois, where the highest reflectances yet observed (> 1.0% Ro) correspond to a complexly faulted and mineralized area with nearby igneous intrusions. Changes in color and intensity of UV fluorescence of liptinites are generally in good agreement with reflectance data. Occurrence and abundance of amorphous organic matter, alginites (mainly Tasmanites), vitrinites, and exinites are facies-dependent. Solid hydrocarbons that occur as pore fillings in fusinite are present mainly in samples from southeastern Illinois. Their presence suggests that hydrocarbon generation and expulsion have occurred in the New Albany in southeastern Illinois. End_of_Article - Last_Page 1575------------