Thermal maturation and oil generation history of Pennsylvanian (Desmoinesian) black shales of Powder River and northern Denver basins

Conference · Fri Sep 01 04:00:00 EDT 1989 · AAPG Bulletin (American Association of Petroleum Geologists); (USA)

OSTI ID:5571044

Clayton, J L; Daws, T A ^[1]

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1. Geological Survey, Denver, CO (USA)

Thin Middle Pennsylvanian (Desmoinesian) organic-rich black shales (cumulative thickness < 50 ft) underlie much of the northern Denver basin and southeastern Powder River basin. In the Powder River basin, these shales are part of the middle member of the Minnelusa Formation. During Desmoinesian time, the present area of the southeastern Powder River basin and Nebraska panhandle was a shallow, at times highly saline, restricted sea. In contrast, in the present area of northeastern Colorado, these black shales were deposited in a sea with normal marine salinity. The authors have evaluated the thermal maturity of the shales using a combination of petrographic and geochemical techniques. In general, thermal maturities are fairly low (mostly equivalent to R{sub 0} about 0.6% or less), although an area of higher heat flow and attendant higher thermal maturity is evident in the southern Nebraska Panhandle area. The authors determined kinetic parameters for oil generation from the shales at several locations in the study area. The activation energy (E{sub a}) distribution for thermal decomposition of kerogen in these shales is highly variable (about 10 kcal/mole range for the average E{sub a}) and can be related to the paleogeography (i.e., the chemical conditions during deposition). An inverse relationship exists between the average E{sub a} for the kerogen breakdown and sulfur content of the shales. The result of this difference in E{sub a} values is that oil generation histories of the shales would be significantly different for a given thermal history even though the organic matter is fairly uniform type II in bulk analysis.

• OSTI ID: 5571044
• Report Number(s): CONF-8910195--
• Conference Information: Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (USA) Journal Volume: 73:9
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020200* -- Petroleum-- Reserves
Geology
&amp; Exploration
BITUMINOUS MATERIALS
BLACK SHALES
CARBONACEOUS MATERIALS
CHATTANOOGA FORMATION
CHEMICAL COMPOSITION
COLORADO
ENERGY SOURCES
FEDERAL REGION VIII
FOSSIL FUELS
FUELS
GEOLOGIC DEPOSITS
GEOLOGIC FORMATIONS
GEOLOGIC STRUCTURES
GEOTHERMAL GRADIENTS
KEROGEN
MATERIALS
MATURATION
MINERAL RESOURCES
MONTANA
NORTH AMERICA
OIL SHALES
ORGANIC MATTER
PENNSYLVANIAN PERIOD
PETROLEUM DEPOSITS
POWDER RIVER BASIN
RESOURCES
SEDIMENTARY BASINS
SOURCE ROCKS
TEMPERATURE GRADIENTS
USA
WYOMING