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Differentiating between biogenic and thermogenic sources of natural gas in coalbed methane reservoirs from the Illinois Basin using noble gas and hydrocarbon geochemistry

By
Myles T. Moore
Myles T. Moore
Divisions of Solid Earth Dynamics and Water, Climate and the Environment, School of Earth Sciences, The Ohio State University, Columbus, OH 43210, USA
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David S. Vinson
David S. Vinson
Department of Geography and Earth Sciences, University of North Carolina-Charlotte, Charlotte, NC 28223, USA
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Colin J. Whyte
Colin J. Whyte
Divisions of Solid Earth Dynamics and Water, Climate and the Environment, School of Earth Sciences, The Ohio State University, Columbus, OH 43210, USA
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William K. Eymold
William K. Eymold
Divisions of Solid Earth Dynamics and Water, Climate and the Environment, School of Earth Sciences, The Ohio State University, Columbus, OH 43210, USA
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Talor B. Walsh
Talor B. Walsh
Department of Earth Sciences, Millersville University, Millersville, PA 17511, USA
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Thomas H. Darrah
Thomas H. Darrah
Divisions of Solid Earth Dynamics and Water, Climate and the Environment, School of Earth Sciences, The Ohio State University, Columbus, OH 43210, USA
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Published:
January 01, 2018

Abstract:

While coalbed methane (CBM) is a significant source of natural gas production globally, uncertainties regarding the proportions of biogenic and thermogenic natural gas in CBM reservoirs still remain. We integrate major gases, hydrocarbon composition, hydrocarbon stable isotopes and noble gases in fluids from 20 producing CBM wells to more accurately constrain the genetic source of natural gases in the eastern Illinois Basin, USA. Previous studies have indicated primarily biogenic production of methane (>99.6%) with negligible contributions from thermogenic natural gases. However, by integrating noble gases, we identify quantifiable (up to 19.2%) contributions of exogenous thermogenic gas in produced gases from the Seelyville and Springfield coal seams. Thermogenic gases are distinguished by a positive relationship between methane, ethane and helium-4, lower C1/C2+, heavier δ13C-CH4, more radiogenic noble gases (4He, 21Ne*, 40Ar*), and lower abundances of atmospherically derived gases (20Ne, 36Ar). Biogenic gases displayed lighter δ13C-CH4, higher C1/C2+, higher levels of atmospheric gases and lower abundances of radiogenic noble gases. Our data suggest that natural gases from a deeper, exogenous thermogenic source likely migrated to the Pennsylvanian-aged coals at an unknown time and later mixed with biogenic methane diluting the geochemical signature of the thermogenic methane within the Springfield and Seelyville coal seams.

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Geological Society, London, Special Publications

From Source to Seep: Geochemical Applications in Hydrocarbon Systems

M. Lawson
M. Lawson
ExxonMobil Upstream Research Company, USA
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M.J. Formolo
M.J. Formolo
ExxonMobil Upstream Research Company, USA
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J.M. Eiler
J.M. Eiler
California Institute of Technology, USA
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Geological Society of London
Volume
468
ISBN electronic:
9781786203687
Publication date:
January 01, 2018

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