Abstract
Pennsylvanian oil and gas accumulations in the southern Paradox basin are in carbonate mounds of Desmoinesian age. Major oil production at Aneth, Ismay, Tohonadla, Gothic Mesa, Anido Creek, and other fields is from algal mounds elongate in a general northwest-southeast direction along the basin shelf. Carbonate reservoirs are associated closely with sapropelic black shale and evaporite, which occur in cyclic repetition in the shelf area and grade basinward to a predominantly salt section. All reservoirs appear to be isolated bodies of porous carbonate, mostly limestone. About 30 oil and gas fields productive from the Pennsylvanian have been found in the Four Corners area; approximately half are classified as stratigraphic and the other half as either structural or structural-stratigraphic. In almost all fields, it can be demonstrated that the accumulation would have formed even if no structural closure were present, although in many fields the oil is localized by subsequent structural growth. The Aneth, Ismay, and Cache fields are primary examples of Paradox basin fields showing major stratigraphic and only minor structural influence on accumulation.
Published Version
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