Controls on bacterial gas accumulations in thick Tertiary coal beds and adjacent channel sandstones, Powder River basin, Wyoming and Montana

Conference · Fri Mar 01 04:00:00 EST 1991 · AAPG Bulletin (American Association of Petroleum Geologists); (United States)

OSTI ID:7271143

Rice, D D; Flores, R M ^[1]

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1. 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--
• Conference Information: Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (United States) Journal Volume: 75:3
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
010600 -- Coal
Lignite
& Peat-- Properties & Composition
03 NATURAL GAS
030300* -- Natural Gas-- Drilling
Production
& Processing
033000 -- Natural Gas-- Properties & Composition
ALKANES
BACTERIA
BIOCONVERSION
CARBONACEOUS MATERIALS
CENOZOIC ERA
CHEMICAL COMPOSITION
CHEMISTRY
COAL
COAL DEPOSITS
COAL RANK
DEGASSING
DESORPTION
DEVELOPED COUNTRIES
ENERGY SOURCES
FEDERAL REGION VIII
FERMENTATION
FLUIDS
FOSSIL FUELS
FUEL GAS
FUELS
GAS FUELS
GASES
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC FORMATIONS
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
HYDROCARBONS
MACERALS
MATERIALS
METHANE
MICROORGANISMS
MINERAL RESOURCES
MONTANA
NATURAL GAS
NATURAL GAS DEPOSITS
NORTH AMERICA
ORGANIC COMPOUNDS
ORIGIN
POWDER RIVER BASIN
PRODUCTION
RESERVES
RESERVOIR ROCK
RESOURCES
ROCKS
SANDSTONES
SEDIMENTARY ROCKS
SORPTION
SORPTIVE PROPERTIES
SURFACE PROPERTIES
TERTIARY PERIOD
USA
WATERSHEDS
WYOMING