Biogenic gas is a major component of global coal bed methane resources. Understanding how to stimulate this process in-situ may help increase reserves and extend well production lifespan. Various studies have started to identify the microbial participants and their putative metabolites, but exact metabolic pathways and rate-limiting steps are not yet defined. Despite the uncertainties in the coal-to-methane process, probable steps can be defined and used for kinetic model development. Methanogen kinetics are reported in literature and provide a foundation for modeling methanogenic systems, but the complexity of coal as a substrate makes the initial hydrolysis and primary fermentation steps especially uncertain. A computational model was developed using a general coal-to-methane mechanism, which simplifies the process to three microbial groups and four intermediates. Acidogens mediate the production of partially soluble organics (PSO) from the coal and subsequently produce acetate, carbon dioxide, and hydrogen from the PSO. The model includes two methanogenic groups which follow either acetoclastic or hydrogenotrophic methanogenesis. Methanogen rate constants were fixed while the hydrolysis and acidogenic steps were fit to experimental and published data. The model was validated by comparing fit parameters to the kinetics published for various anaerobic microbial systems (e.g. polyaromatic hydrocarbon removal, long chain fatty acid utilization, etc.). Model results will be used to speculate on rate limiting steps, and the potential impact of various stimulation strategies will be explored.

Use of a kinetic model to identify rate-limitations for biological methane production from coal

249th National Meeting (2015)

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