Nature of natural gas in anomalously thick coal beds, Powder River basin, Wyoming

Conference · Fri Sep 01 00:00:00 EDT 1989 · AAPG Bulletin (American Association of Petroleum Geologists); (USA)

OSTI ID:5495790

Rice, D D; Flores, R M ^[1]

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1. Geological Survey, Denver, CO (USA)

Anomalously thick coal beds (as much as 250 ft thick) occur in the Paleocene Tongue River Member of the Fort Union Formation in the Powder River basin, Wyoming. These laterally discontinuous coal beds were deposited in raised, ombrotrophic peat bogs of fluvial environments. The coal beds include the Anderson-Canyon, Wyodak-Anderson, and Big George zones in the Powder River-Recluse area, Gillette area, and central part of the basin, respectively. The coal resources in these areas are approximately 155 billion short tons. The average maceral composition of the coals is 88% huminite (vitrinite), 5% liptinite, and 7% inertinite. The coals vary in rank from subbituminous C to A (R{sub 0} values of 0.4 to 0.5%). Natural gas desorbed and produced from the coal beds and adjacent sandstones is composed mainly of methane with lesser amounts of CO{sub 2} (less than 10%). The methane is isotopically light ({delta}{sup 13}C{sup 1} values of {minus}56.7 to {minus}60.9%). Based on the chemical and isotopic composition of the gases and on the low rank of the coals, the gases are interpreted to be microbial in origin: they were generated by anaerobic bacteria that broke down the coals at low temperatures, prior to the main phase of thermogenic methane generation by devolatilization. The adsorbed amounts of methane-rich microbial gas per unit of coal in the Powder River basin are relatively low compared to amounts of thermogenic coal-bed gases from other basins. However, the total coal-bed gas resource is considered to be large (as much as several trillion cubic feet) because of the vast coal resources.

• OSTI ID: 5495790
• Report Number(s): CONF-8910195-; CODEN: AABUD
• Journal Information: AAPG Bulletin (American Association of Petroleum Geologists); (USA), Vol. 73:9; Conference: AAPG Rocky Mountain Section meeting, Albuquerque, NM (USA), 1-4 Oct 1989; ISSN 0149-1423
• Country of Publication: United States
• Language: English

Related Subjects

03 NATURAL GAS
POWDER RIVER BASIN
COAL DEPOSITS
NATURAL GAS DEPOSITS
WYOMING
CARBON DIOXIDE
GEOLOGIC FORMATIONS
METHANE
SOURCE ROCKS
TERTIARY PERIOD
ALKANES
CARBON COMPOUNDS
CARBON OXIDES
CENOZOIC ERA
CHALCOGENIDES
FEDERAL REGION VIII
GEOLOGIC AGES
GEOLOGIC DEPOSITS
HYDROCARBONS
MINERAL RESOURCES
MONTANA
NORTH AMERICA
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
RESOURCES
USA
030200* - Natural Gas- Reserves
Geology
& Exploration