Controls on bacterial gas accumulations in thick Tertiary coal beds and adjacent channel sandstones, Powder River basin, Wyoming and Montana
- U.S. Geological Survey, Denver, CO (United States)
Coal beds, as much as 250 ft thick, and adjacent sandstones in the Paleocene Tongue River Member of the Fort Union Formation are reservoirs for coal-derived natural gas in the Powder River basin. The discontinuous coal beds were deposited in raised, ombrotrophic peat bogs about 3 mi{sup 2} in size, adjoining networks of fluvial channels infilled by sand. Coal-bed thickness was controlled by basin subsidence and depositional environments. 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 o} values of 0.4 to 0.5%). Although the coals are relatively low rank, they display fracture systems. Natural gas desorbed and produced from the coal beds and adjacent sandstones is composed mainly of methane with lesser amount of Co{sub 2} ({lt}10%). The methane is isotopically light and enriched in deuterium. The gases are interpreted to be generated by bacterial processes and the fermentation pathway, prior to the main phase of thermogenic methane generation by devolatilization. Large amounts of bicarbonate water generated during early stages of coalification will have to be removed from the fracture porosity in the coal beds before desorption and commercial gas production can take place. Desorbed amounts of methane-rich, bacterial gas in the Powder River basin are relatively low ({lt}60 Scf/ton) compared to amounts of thermogenic coal-bed gases (hundreds of Scf/ton) from other Rocky Mountain basins. However, the total coal-bed gas resource in both the coal beds and the adjacent sandstones is considered to be large (as much as 40 Tcf) because of the vast coal resources (as much as 1.3 trillion tons).
- OSTI ID:
- 7271143
- Report Number(s):
- CONF-910403-; CODEN: AABUD
- Journal Information:
- AAPG Bulletin (American Association of Petroleum Geologists); (United States), Vol. 75:3; Conference: Annual meeting of the American Association of Petroleum Geologists (AAPG), Dallas, TX (United States), 7-10 Apr 1991; ISSN 0149-1423
- Country of Publication:
- United States
- Language:
- English
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01 COAL, LIGNITE, AND PEAT
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PRODUCTION
NATURAL GAS
CHEMICAL COMPOSITION
POWDER RIVER BASIN
COAL DEPOSITS
NATURAL GAS DEPOSITS
BACTERIA
COAL
COAL RANK
DEGASSING
FERMENTATION
GEOCHEMISTRY
GEOLOGIC FORMATIONS
GEOLOGIC FRACTURES
MACERALS
ORIGIN
RESERVES
RESERVOIR ROCK
SANDSTONES
SORPTIVE PROPERTIES
TERTIARY PERIOD
ALKANES
BIOCONVERSION
CARBONACEOUS MATERIALS
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DEVELOPED COUNTRIES
ENERGY SOURCES
FEDERAL REGION VIII
FLUIDS
FOSSIL FUELS
FUEL GAS
FUELS
GAS FUELS
GASES
GEOLOGIC AGES
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HYDROCARBONS
MATERIALS
MICROORGANISMS
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MONTANA
NORTH AMERICA
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030300* - Natural Gas- Drilling
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033000 - Natural Gas- Properties & Composition
010600 - Coal
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