AmericanChemicalSociety.com

Coal seams from the Powder River basin generate economic quantities of natural gas, with over 20,000 wells now producing. Geochemical indicators suggest this gas is predominantly microbial generated methane. Isotopic indicators from the wells sampled for this study indicate the gas forms via the CO2-reduction pathway, although shallow wells from the margin of the basin have indicated acetate fermentation as the major pathway. Early analysis of clone libraries from 16s rRNA identifies a complex community of fermenters, acetogens and methanogens, similar to the communities found in the Antrim Shale, Michigan Basin. Analyses of the coal from cores located near the producing wells indicate significant microbial degradation of the organic matter. Two of the sampled wells that had measurable concentration of sulfate within the formation water also produced clones associated with sulfate-reducing bacteria. This is likely an inhibitor of methanogenic activity, and may be related to the varying productivity of the coal. Ongoing work is focusing on the relationships among community diversity, environmental conditions and rock properties. Data is also being assembled for analysis of production rates (both gas and water) associated with each well. Correlations are also being made among the microbial populations extracted from coalbeds in the Illinois Basin, and from coals within the San Juan Basin, both areas where the geochemistry of gas and water suggest microbial generation of methane. In the laboratory, a series of cultivation experiments are underway, exploring the rates of methane production with varied substrate sources (coal, shale, acetate, H2-CO2). Together, these results will serve to further illuminate the processes that extant microbial communities generate significant gas deposits from ancient organic sources.