Methanogenic Microbial Degradation of Organic Matter in Indiana Coal Beds

Dariusz Strapoc¹, Flynn Picardal², Courtney Turich³, Irene Schaperdoth⁴, Jennifer Macalady⁴, Julius S. Lipp⁵, Yu-Shih Lin⁵, Tobias F. Ertefai⁵, Florence Schubotz⁵, Kai-Uwe Hinrichs⁵, Maria Mastalerz¹, and Arndt Schimmelmann^6
1Geological Sciences, Indiana University, Blomington, IN
²School of Public and Environmental Affairs, Indiana University, Bloomington, IN
³Skidaway Institute of Oceanography, Savannah, GA
⁴Geological Sciences, Penn State University, Unversity Park, PA
⁵Geosciences, University of Bremen, Bremen, Germany
⁶Indiana Geological Survey, Indiana University, Bloomington, IN

We investigated the phylogenic and geochemical characteristics of biogenic coalbed methane (CBM) in the Indiana part of the Illinois Basin to identify the organisms responsible for methane generation and to determine the biogeochemical constraints on production of methanogenic substrates, such as H₂ and CO₂. 16S rRNA analysis of in-situ microbial community and methanogen enrichments indicate that Methanocorpusculum is the dominant methanogenic genus. This microorganism was characterized by its distribution of intact polar cell membrane lipids (IPLs) and by scanning electron microscopy. Typical characteristics of Methanocorpusculum were rapid growth in the H₂ and CO₂ environment, small 0.4 μm spherical cells, and a 2:1 ratio of diethers to tetraethers in the cell membrane. Within the clone library of water co-produced from a CBM well, we also found species capable of anaerobic degradation of a variety of molecules, including polyaromatic, aromatic, and aliphatic hydrocarbons. Oil extracted from co-produced coalbed water shows a high level of biodegradation. We calculated free energies available for in-situ subsurface conditions for CO₂-reduction and acetoclastic methanogenesis, homoacetogenesis, and syntrophic acetate oxidation that represent terminal microbial biodegradation reactions. Methanogenesis via CO₂-reduction appears to be the dominant terminal biodegradation process affecting coal organic matter. We suggest that post-uplift influx of fresh water, most likely during inter- and post-glacial periods, decreased the salinity of the original basinal brine and allowed inoculation of previously sterile Indiana coals with a diverse biodegrading microbial community. Further integrated biogeochemical analysis will more precisely define the role of the microbial community on the rate-limiting steps of biogenic methane formation.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas