Recognition of hydrocarbon expulsion using well logs: Bakken Formation, Williston Basin
- Exxon Production Research Co., Houston, TX (USA)
- Exxon Co., U.S.A., Houston, TX (USA)
The Upper Mississippian-Lower Devonian Bakken Formation forms a source/carrier/reservoir system in the Williston basin. Hydrocarbon expulsion within the Bakken has been identified by overlaying sonic and resistivity logs. Typically, these curves track in organically lean, water-saturated mudrocks because both respond mainly to porosity; however, in thermally mature organic-rich rocks and hydrocarbon reservoirs or carrier beds, the curves separate due to the anomalously high resistivity associated with replacement of pore water by hydrocarbons. Sonic/resistivity-log overlays for wells throughout the Montana and North Dakota parts of the Williston basin reveal significant increases and maximum in-curve separation within the middle siltstone member of the Bakken at subsurface temperatures of about 170 and 200{degree}F, respectively. Sequence-stratigraphic characteristics of the Bakken define the framework within which the expulsion process operates. The organic-rich upper and lower shale members represent the transgressive and early highstand systems tracts of two adjacent depositional sequences. A sequence boundary within the intervening middle siltstone member separates nearshore siltstone and sandstone of the late highstand systems tract in the lower sequence from cross-bedded subtidal to intertidal sandstones of the lowstand systems tract in the upper sequence. Reservoir properties vary across this sequence boundary. The authors attribute the log separation in the siltstone member to hydrocarbons expelled from the adjacent shales. Abrupt shifts in several geochemical properties of the shale members, indicative of hydrocarbon generation occur over the same subsurface temperature range as the rapid increase in log separation in the middle siltstone, thus indicating the contemporaneity of generation and expulsion.
- OSTI ID:
- 7034148
- Report Number(s):
- CONF-900605-; CODEN: AABUD
- Journal Information:
- AAPG Bulletin (American Association of Petroleum Geologists); (USA), Vol. 74:5; Conference: Annual convention and exposition of the American Association of Petroleum Geologists, San Francisco, CA (USA), 3-6 Jun 1990; ISSN 0149-1423
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
03 NATURAL GAS
58 GEOSCIENCES
NATURAL GAS DEPOSITS
EXPLORATION
ORIGIN
PETROLEUM DEPOSITS
WILLISTON BASIN
CARBONIFEROUS PERIOD
DEVONIAN PERIOD
GEOLOGIC FORMATIONS
MATURATION
RESERVOIR ROCK
SANDSTONES
SHALES
SILTSTONES
SOURCE ROCKS
WELL LOGGING
GEOLOGIC AGES
GEOLOGIC DEPOSITS
MINERAL RESOURCES
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580000 - Geosciences