Microbial methane from subsurface organic-rich units such as coals and shale support approximately 5% of the United States and Canada's energy needs. In the deep subsurface, microbial methane is formed by the metabolism of primarily CO2, H2, and acetate by methanogens. These metabolites are the by-products of multi-step biodegradation of complex organic matter by microbial consortia. This study investigates microbial methane in the Illinois Basin, which is present in organic-rich shallow glacial sediments (surficial), Pennsylvanian coals (up to 600 m depth), and the Upper Devonian New Albany Shale (up to 900 m depth). Findings from the study show that hydrogeochemical conditions are favorable for methanogenesis in each reservoir, with a decrease in groundwater flushing rates corresponding to a decrease in average reservoir depth and an increase in carbon isotopic fractionation. The deeper reservoirs (coals and shale) were paleopasteurized, necessitating re-inoculation by methanogens. The microbes were likely advectively transported from shallow sediments into the coals and shale, where areas of microbial methanogenesis correlate with freshwater recharge. The recharge in the shale was primarily sourced from paleoprecipitation with minor contributions from glacial meltwater during the Pleistocene (4He ages). All areas sampled in the shale were affected by Pleistocene recharge, however groundwater ages in areas of microbial methanogenesis are younger (average 0.33 Ma) than areas with thermogenic methane (average 1.0 Ma). Estimates of in-situ microbial methane production rates for the shale (10-1000 TCF/Ma) are 104-106 times slower than laboratory rates. Only limited biodegradation is observed in the shale. In-situ stimulation of methane production may be most effective if aimed at increasing production of the supporting microbial consortia as well as methanogens. Trace metal concentrations in the shale are below known levels of inhibition or enhancement, with the exception of Fe, suggesting that microbial methanogenesis is not repressed by any of the measured trace metals and may be improved with the addition of Ag, Co, Cr, Ni, and Zn.

The New Albany Shale is an Upper Devonian organic-rich gas shale located in the Illinois Basin. A factor influencing gas production from the shale is the natural fracture system. I test the hypothesis that a combination of outcrop and core observations, rock property tests, and geomechanical modeling can yield an accurate representation of essential natural fracture attributes that cannot be obtained from any of the methods alone. Field study shows that New Albany Shale outcrops contain barren (free of cement) joints, commonly oriented in orthogonal sets. The dominant set strikes NE-SW, with a secondary set oriented NNW-SSE. I conclude that the joints were likely created by near-surface processes, and thus are unreliable for use as analogs for fractures in the reservoir. However, the height, spacing, and abundance of the joints may still be useful as guides to the fracture stratigraphy of the New Albany Shale at depth. The Clegg Creek and Blocher members contain the highest fracture abundance. Fractures observed in four New Albany Shale cores are narrow, steeply-dipping, commonly completely sealed with calcite and are oriented ENE-WSW. The Clegg Creek and Blocher members contain the highest fracture abundance, which is consistent with outcrop observations. Fractures commonly split apart along the wall rock-cement interface, indicating they may be weak planes in the rock mass, making them susceptible to reactivation during hydraulic fracturing. Geomechanical testing of six core samples was performed to provide values of Young’s modulus, subcritical index, and fracture toughness as input parameters for a fracture growth simulator. Of these inputs, subcritical index is shown to be the most influential on the spatial organization of fractures. The models predict the Camp Run and Blocher members to have the most clustered fractures, the Selmier to have more evenly-spaced fractures, and the Morgan Trail and Clegg Creek to have a mixture of even spacing and clustering. The multi-faceted approach of field study, core work, and geomechanical modeling I used to address the problem of fracture characterization in the New Albany Shale was effective. Field study in the New Albany presents an opportunity to gather a large amount of data on the characteristics and spatial organization of fractures quickly and at relatively low cost, but with questionable reliability. Core study allows accurate observation of fracture attributes, but has limited coverage. Geomechanical modeling is a good tool for analysis of fracture patterns over a larger area than core, but results are difficult to corroborate and require input from outcrop and core studies. / text