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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
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The Cottonwood and No Water Creek fields produce from a common carbonate reservoir formed by a facies change from shelf carbonates on the west to continental redbeds on the east. Production is from the Ervay Member of the Permian Phosphoria Formation.
Carbonate sediments of the Ervay are analogous to carbonate sediments of the Persian Gulf suggesting similar depositional environments. Paleoenvironments in the study area were determined by thin-section analyses and include salt flats, mud banks, mud flats, lagoons, and green algal banks. Carbonate sediments were deposited in an embayment on a broad stable shelf bordered by low continental areas on the east and the miogeosyncline on the west. Arid and warm climatic conditions prevailed over most of the area allowing for rapid evaporation in the nearshore areas. Green algal banks developed along sub-hinge lines (or topographic highs) on the shelf. These banks provide the best reservoir conditions and possibly the best production at No Water Creek field.
The Ervay throughout the subject area is dolomitized. Dolomitization was penecontemporaneous with deposition and anhydrite precipitation. Chert and collophane are common accessory minerals and increase in percentage westward. Anhydrite increases in percentage eastward.
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