Stimulation of microbial methanogenesis in organic strata (coal, black shale, petroleum) has great potential to produce usable natural gas from unavailable resources such as unrecoverable coal beds, depleted shale gas and petroleum reservoirs, and energy waste (coal slurry, shale core cuttings). Knowledge of the consortium of microorganisms, and decomposition pathways involved in the production of microbial natural gas from organic strata and energy waste material is essential for developing effective microbial stimulation approaches. In this study, the mechanisms involved in the microbial production of methane from coal were examined, with the goal of increasing production of methane from coal. Field studies of formation water and gas chemistry and isotopic composition, and microbial populations in the Powder River Basin (WY and MT) suggest that methanogenesis by acetate fermentation dominates on the margins of the basin where hydrologic recharge occurs, while methanogenesis by CO<sub>2</sub> reduction dominates in the center of the basin. Organic substances present in the formation water (alkanes, simple aromatic substances, and long-chain fatty acids) are important intermediates in biodegradation of coal geopolymers to methane. Important microbial groups observed in coal and formation water include Proteobacteria and Firmicutes. Attempts to identify methanogens present in coalbeds using qPCR and 16SPCR have been previously hampered by generally low abundances of methanogens. Laboratory studies used fresh subbituminous coal samples from cores from the Powder River Basin (WY and MT), and the Gulf Coast (TX) in laboratory bioreactor experiments to generate methane, using both endemic microbial populations and a bioassay we developed. Methane production curves over time (40-60 days) involved an initial lag period of 14 days, during which substrate (long chain fatty acids, acetate, etc.) and microbial population buildup occurred. The lag phase was followed by an exponential growth phase (active methane production from substrate), and then a phase where methane production reached a plateau (equilibrium between substrate production and utilization). Approaches for stimulating microbial activity have focused on increasing coal bioavailability through several mild treatment approaches, and increasing microbial populations through nutrient addition. A test site in the Powder River Basin, Montana is being evaluated for field testing of stimulation approaches.

Biodegradation pathways and organic intermediates in the conversion of coal geoploymers to methane

249th National Meeting (2015)

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