Coupled hydrology and biogeochemistry of Paleocene–Eocene coal beds, northern Gulf of Mexico

Research Article| July 01, 2010 Coupled hydrology and biogeochemistry of Paleocene–Eocene coal beds, northern Gulf of Mexico Jennifer C. McIntosh; Jennifer C. McIntosh † 1Department of Hydrology and Water Resources, and U.S. Geological Survey Adjunct Research Geologist, University of Arizona, Tucson, Arizona 85721, USA †E-mail: mcintosh@hwr.arizona.edu Search for other works by this author on: GSW Google Scholar Peter D. Warwick; Peter D. Warwick § 2U.S. Geological Survey, 956 National Center, Reston, Virginia 20192, USA §E-mail: pwarwick@usgs.gov Search for other works by this author on: GSW Google Scholar Anna M. Martini; Anna M. Martini # 3Department of Geology, Amherst College, Amherst, Massachusetts 01002, USA #E-mail: ammartini@amherst.edu Search for other works by this author on: GSW Google Scholar Stephen G. Osborn Stephen G. Osborn * 1Department of Hydrology and Water Resources, and U.S. Geological Survey Adjunct Research Geologist, University of Arizona, Tucson, Arizona 85721, USA *E-mail: sosborn@hwr.arizona.edu Search for other works by this author on: GSW Google Scholar GSA Bulletin (2010) 122 (7-8): 1248–1264. https://doi.org/10.1130/B30039.1 Article history received: 23 Feb 2009 rev-recd: 18 Jun 2009 accepted: 22 Jun 2009 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Jennifer C. McIntosh, Peter D. Warwick, Anna M. Martini, Stephen G. Osborn; Coupled hydrology and biogeochemistry of Paleocene–Eocene coal beds, northern Gulf of Mexico. GSA Bulletin 2010;; 122 (7-8): 1248–1264. doi: https://doi.org/10.1130/B30039.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Thirty-six formation waters, gas, and microbial samples were collected and analyzed from natural gas and oil wells producing from the Paleocene to Eocene Wilcox Group coal beds and adjacent sandstones in north-central Louisiana, USA, to investigate the role hydrology plays on the generation and distribution of microbial methane. Major ion chemistry and Cl−Br relations of Wilcox Group formation waters suggest mixing of freshwater with halite-derived brines. High alkalinities (up to 47.8 meq/L), no detectable SO4, and elevated δ13C values of dissolved inorganic carbon (up to 20.5‰ Vienna Peedee belemnite [VPDB]) and CO2 (up to 17.67‰ VPDB) in the Wilcox Group coals and adjacent sandstones indicate the dominance of microbial methanogenesis. The δ13C and δD values of CH4, and carbon isotope fractionation of CO2 and CH4, suggest CO2 reduction is the major methanogenic pathway. Geochemical indicators for methanogenesis drop off significantly at chloride concentrations above ∼1.7 mol/L, suggesting that high salinities inhibit microbial activity at depths greater than ∼1.6 km. Formation waters in the Wilcox Group contain up to 1.6% modern carbon (A14C) to at least 1690 m depth; the covariance of δD values of co-produced H2O and CH4 indicate that the microbial methane was generated in situ with these Late Pleistocene or younger waters. The most enriched carbon isotope values for dissolved inorganic carbon (DIC) and CO2, and highest alkalinities, were detected in Wilcox Group sandstone reservoirs that were CO2 flooded in the 1980s for enhanced oil recovery, leading to the intriguing hypothesis that CO2 sequestration may actually enhance methanogenesis in organic-rich formations. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.