Phospholipid Evidence for Methanogenic Archaea and Sulfate-Reducing Bacteria in Coalbed Methane Wells in the Powder River Basin, Wyoming
The Powder River Basin (PRB) comprises roughly 22,000 square miles in northeastern Wyoming and southeastern Montana; it is a major source of coal and natural gas in the Rocky Mountain and Great Plains regions. The coalbed methane (CBM) produced from Paleocene Fort Union Formation coals in the PRB is thought primarily to be of bacterial origin due to its low δ13C values of -51-82‰. Determination of the timing of methanogenesis, however, requires a methodology suitable for identifying viable methanogenic microorganisms. Here we provide evidence of living methanogenic Archaea and sulfate-reducing bacteria collected from co-produced water from CBM wells using phospholipid fatty acid (PLFA) and phospholipid ether lipid (PLEL) analyses. Twelve producing wells were sampled in May, 2007, and two in November, 2008 using a high-pressure filtering apparatus. PLFAs were analyzed as fatty acid methyl esters and PLELs analyzed by their liberated core components using gas chromatography/mass spectrometry. Phospholipid analyses revealed an ecosystem dominated by Archaea, as the Archaeal isoprenoid phytane was the dominant phospholipid observed in nine of the wells sampled. Total microbial biomass estimates ranged from 1.1 x10^6 cells/L to 8.3 x10^7 cells/L, with the proportion of Archaeal cells ranging from 77.5 to 99.7 percent. In addition, the biomarkers 10me16:0, and cy17:0, considered to be indicative of sulfate-reducing bacteria, were observed in 5 wells. The dominance of lipids from living Archaea in co-produced waters from CBM wells provides evidence supporting a recent origin of gas in the PRB coals.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009