Faulted shoreline and tidal deposits in the Moenkopi Formation of the Grassy Trail Creek field, Utah

Conference · Sat Jun 01 00:00:00 EDT 1991 · AAPG Bulletin (American Association of Petroleum Geologists); (United States)

OSTI ID:6093814

Allison, M L ^[1]; Lutz, S J ^[2]

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1. Utah Geological and Mineral Survey, Salt Lake City (United States)
2. Univ. of Utah Research Inst., Salt Lake City (United States)

The Grassy Trail Creek field produces 40{degrees} API oil and minor gas from shallow marine sandstones of the Triassic Moenkopi Formation on the north-plunging nose of the San Rafael swell in central Utah. Production is controlled by a combination of stratigraphic variations and minor north-south-trending faults. Although fracture permeability enhances production of the reservoir, some faults act as barriers to fluid migration, segmenting the area into productive and dry fault blocks. Horizontal drilling techniques developed in this field in the early 1980s resulted in significantly better production. Log analyses indicate the main reservoir is a complex stack of this thin tidal channel sandstones. Isochore maps of the A and B zones indicate thickened meanders that form localized reservoir pods that are vertically offset. The distribution of isochore thicks appears to represent deposition along a northwest-southeast-trending shoreline fed by sediments from the northeast. There is potential for field extensions in similar deposits along this paleoshoreline. The Moenkopi Formation, long thought to be self-sourcing, may contain oil generated in Precambrian sediments equivalent to the Late Proterozoic Chuar Group. Presence of this older oil would have required migration from Precambrian sedimentary rocks surrounding the San Rafael swell.

• OSTI ID: 6093814
• Report Number(s): CONF-9107109-; CODEN: AABUD
• Journal Information: AAPG Bulletin (American Association of Petroleum Geologists); (United States), Vol. 75:6; Conference: American Association of Petroleum Geologists (AAPG) Rocky Mountain Section meeting, Billings, MT (United States), 28-31 Jul 1991; ISSN 0149-1423
• Country of Publication: United States
• Language: English

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02 PETROLEUM
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GEOLOGIC FAULTS
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GEOLOGIC FRACTURES
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