ENRICHMENT AND CHARACTERIZATION OF METHANOGENIC CONSORTIA FROM COALBED METHANE WELLS IN THE POWDER RIVER BASIN

Field water samples from coalbed methane wells in the Powder River Basin of Wyoming tested positive for the presence of living microbial communities capable of producing methane (methanogenic consortia). If these communities are capable of producing methane from coal present in the reservoir, this suggests an opportunity to maintain or enhance coalbed methane reserves by maintaining/enhancing the activity of existing methanogenic consortia in-situ. In this study, wellbore water was collected from the Fort Union formation at depths of 737 to 778 ft using a sterile sample container lowered on a wireline. This sample tested positive for methanogens in the laboratory using an enrichment culture technique under strict anaerobic conditions. These methanogens produced methane when acetate or methanol were provided as the sole carbon-energy substrate, but did not produce methane when a H2-CO2 headspace provided the sole carbon-energy source. The bacterial consortium present in this sample was then shown to produce methane in a defined microbial medium using Wyodak coal as the sole carbon substrate. At 30 °C, methane production rates were on the order of 5 SCF/ton coal/day; in comparison, total methane reserves in the Powder River basin are approximately 70 SCF/ton coal. This consortium was subsequently maintained in the laboratory using coal as the sole carbon-energy substrate; this maintenance culture was then used to test the effects of temperature, pH, and coal particle size on methane production from coal. When temperatures were increased above the reservoir temperature in the laboratory, total methane production from coal increased by 54%; similarly, when the culture medium pH was adjusted to values lower than the native reservoir water, methane production increased by 68%. Increasing the coal particle surface area via smaller particle size increased methane production rates by over 200%. These results suggest that coal solubility and/or dissolution of key coal substrates may potentially limit real-time in-situ methanogenesis.