Evaluation of Cottonwood Creek field complex, Bighorn basin, Wyoming
Most of the 83 million bbl of oil produced from Cottonwood Creek and associated fields (Worland, Rattlesnake, South Frisby) is from a suite of peritidal dolomite facies that were deposited in and on the flanks of an ancient estuarine system. Isopach and facies maps suggest that the Tensleep fault and related northwest-southeast-oriented basement fault blocks, controlled the formation of this estuary during Late Pennsylvanian/Early Permian time and the pattern of late Ervay deposition within the estuary. Upper Ervay pisolitic and algal-laminated units, along with intraclast grainstones, map as thick (40 to 90 ft), 1 to 2-mi wide and 2 to 5-mi long pods that represent a northwest-southeast peninsular system of islands. The thickest (i.e., central and highest) portions of these islands are made up of extensively altered pisolitic, brecciated units whose porosity systems were destroyed by aragonite and calcite cementation during periodically low sea level stands. The thinner margins of these island pods are made up of reservoir-quality peritidal fenestral fabric, algal-laminated units, and intraclast grainstones that were subjected to significantly less cementation because of less-frequent exposure. Permeability in these units may be enhanced by preferential fracturing because they were deposited along paleostructural zones of weakness. As a result of these depositional, diagenetic, and fracture patterns, cumulative production is commonly much higher (> 200,000 bbl/well) from the flank positions of these pods. Lagoonal dolomite mudstones and red-bed/evaporite sequences were deposited between and behind these islands, respectively, and form the major updip hydrocarbon seals.
- Research Organization:
- Lithologic and Stratigraphic Solutions, Inc., Denver, CO
- OSTI ID:
- 7042333
- Report Number(s):
- CONF-8609129-
- Journal Information:
- Am. Assoc. Pet. Geol., Bull.; (United States), Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Vol. 70:8; ISSN AAPGB
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
020200* -- Petroleum-- Reserves
Geology
& Exploration
ALKALINE EARTH METAL COMPOUNDS
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CARBON COMPOUNDS
CARBONATE MINERALS
CARBONATES
DEPOSITION
DIAGENESIS
DOLOMITE
FEDERAL REGION VIII
GEOLOGIC DEPOSITS
GEOLOGIC FAULTS
GEOLOGIC FORMATIONS
GEOLOGIC FRACTURES
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
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MAGNESIUM CARBONATES
MAGNESIUM COMPOUNDS
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NORTH AMERICA
OIL FIELDS
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PERMEABILITY
PETROLEUM DEPOSITS
RESERVOIR ROCK
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USA
WYOMING