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

Jennifer C. McIntosh, Peter D. Warwick, Anna M. Martini and Stephen G. Osborn
Coupled hydrology and biogeochemistry of Paleocene-Eocene coal beds, northern Gulf of Mexico
Geological Society of America Bulletin (July 2010) 122 (7-8): 1248-1264


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 (super -) 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 SO (sub 4) , and elevated delta (super 13) C values of dissolved inorganic carbon (up to 20.5 per mil Vienna Peedee belemnite [VPDB]) and CO (sub 2) (up to 17.67 per mil VPDB) in the Wilcox Group coals and adjacent sandstones indicate the dominance of microbial methanogenesis. The delta (super 13) C and delta D values of CH (sub 4) , and carbon isotope fractionation of CO (sub 2) and CH (sub 4) , suggest CO (sub 2) reduction is the major methanogenic pathway. Geochemical indicators for methanogenesis drop off significantly at chloride concentrations above approximately 1.7 mol/L, suggesting that high salinities inhibit microbial activity at depths greater than approximately 1.6 km. Formation waters in the Wilcox Group contain up to 1.6% modern carbon (A (super 14) C) to at least 1690 m depth; the covariance of delta D values of co-produced H (sub 2) O and CH (sub 4) 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 CO (sub 2) , and highest alkalinities, were detected in Wilcox Group sandstone reservoirs that were CO (sub 2) flooded in the 1980s for enhanced oil recovery, leading to the intriguing hypothesis that CO (sub 2) sequestration may actually enhance methanogenesis in organic-rich formations.

ISSN: 0016-7606
EISSN: 1943-2674
Serial Title: Geological Society of America Bulletin
Serial Volume: 122
Serial Issue: 7-8
Title: Coupled hydrology and biogeochemistry of Paleocene-Eocene coal beds, northern Gulf of Mexico
Affiliation: University of Arizona, Department of Hydrology and Water Resources, Tucson, AZ, United States
Pages: 1248-1264
Published: 201007
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 92
Accession Number: 2010-050198
Categories: HydrogeologyHydrochemistry
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., 3 tables, sketch maps
N31°00'00" - N33°00'00", W94°00'00" - W90°00'00"
Secondary Affiliation: U. S. Geological Survey, USA, United StatesAmherst College, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201027
Program Name: USGSOPNon-USGS publications with USGS authors
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