Characterization of a methanogenic consortium enriched from a coalbed methane well in the Powder River Basin, U.S.A.

Well-bore water samples from the Fort Union Formation in the Powder River Basin of Wyoming tested positive for the presence of living microbial communities capable of generating methane from Wyodak coal under laboratory conditions. The methanogens in this consortium produced methane from acetate and methanol, but did not produce methane from a H2–CO2 headspace. This was consistent with a phylogenetic analysis of archaeal 16S ribosomal deoxyribonucleic acid (rDNA) sequences from the enrichment culture, which revealed just two phylotypes, both closely related to Methanosarcina mazei. Phylogenetic analysis of bacterial 16S ribosomal ribonucleic acid (rRNA) genes revealed phylotypes similar to the acetogens Acidaminobacter hydrogenoformans and Syntrophomonas sp., and to known fermentative species. This methane-producing consortium was maintained on a defined microbial medium supplemented with Wyodak coal plus 50 mg/L yeast extract as the sole carbon substrates. At 22 °C, the maximum methane production rate was 0.084 m3/t coal/day (2.7 scf/ton/day); in comparison, total methane reserves in the Powder River Basin are approximately 1.6 to 2.2 m3/t (50 to 70 scf/ton). When the incubation temperature was increased from 22 °C to 38 °C, the rate of methane production increased by 300%; similarly, when the culture medium pH was lowered from 7.4 to 6.4, the methanogenesis rate increased by 680%. Increasing the coal particle surface area by 890% via smaller particle size increased methane production rates by over 200%. Microbial methane production in coal slurries was also enhanced by the addition of the solvent N,N-dimethylformamide (DMF). These results suggest an opportunity to enhance coalbed methane reserves by stimulating the activity of existing methanogenic consortia in-situ; in particular, reservoir treatments that enhance coal solubility and dissolution rates may be beneficial.