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AAPG Bulletin

Abstract


Volume: 52 (1968)

Issue: 3. (March)

First Page: 528

Last Page: 528

Title: Anatomy of a Giant--Oklahoma City Field: ABSTRACT

Author(s): Lloyd E. Gatewood

Article Type: Meeting abstract

Abstract:

Oklahoma City field, Oklahoma County, Oklahoma, was discovered in 1928 by the drilling of a wildcat well on a mapped 100-ft surface closure. Today this field ranks among the largest 10 oil fields in the United States. Its structural growth is allied closely to the stages of evolution of the Anadarko basin. Growth probably commenced in Cambrian time, and definitely took place from Ordovician through Early Pennsylvanian time as a result of subsidence in the Anadarko basin. This subsidence caused faulting and compressional folding, the most pronounced of which took place near the northeast rim of the basin. In that area, folds and faults in the Anadarko basin intersected the southern end of a buried mobile basement feature, the Nemaha ridge. The presence of this ridge not on y influenced the position of the Oklahoma City field structure, but also its size, shape, and structural complexity.

The structure was folded, faulted, and truncated more or less contemporaneously. Approximately 2,000 ft of Ordovician-Pennsylvanian sediments was removed from the top; Pennsylvanian sediments above the unconformity overlie rocks as old as Ordovician. The trap is big--12 mi long, and having 1,000 ft of closure. A 2,000-ft, down-to-the-east fault prevented lateral migration of oil from the fold. The Pennsylvanian above the unconformity allowed only limited upward migration. Relief was so prominent and growth so continuous, even after truncation and burial, that the fold provided an ideal environment for development and trapping of oil and gas in the numerous shallow Pennsylvanian sandstones on the irregular surface of the fold. Traps within the Pennsylvanian sandstones include pinchouts fault traps, and channel deposits.

The discovery well produced from Ordovician Arbuckle dolomite, the oldest pre-Pennsylvanian rocks on the crest of the structure beneath the unconformity. The most prolific production has been from the Wilcox Sand (basal Simpson) on the lowest part of the structure along the west flank, nearest the common water table. More than 20 different zones are productive from Ordovician Arbuckle to Late Pennsylvanian. Arbuckle and lower Simpson oil zones have a water drive.

Production from the Wilcox Sand was 350 million bbl of oil and 820 Bcf of gas through 1939, at which time the pressure in the Wilcox zone was reduced to atmospheric. Since 1939 the natural water drive has not been effective and natural gravity drainage has resulted in the production of an additional 186,370,000 bbl of oil. Estimated Wilcox oil in place is 1,072,000,000 bbl.

This field is unique in that it has been for 40 yr a model and proving ground for exploration techniques and producing technology; for modern proration rules and laws; for drilling and testing techniques in deep rotary wells; and for establishing the standards for formation evaluation and reserve estimates. Developments within a major city furnished the excitement caused by many "wild" wells like "Wild Mary Sudik," but joy accrued to the economic infusion which came during the worst days of the depression.

It is a billion-barrel field, having already produced more than that amount of oil and oil-equivalent gas. Of additional importance is the influence which this field has had in the finding and development of great quantities of oil and gas in adjacent areas of Oklahoma and throughout the world.

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Copyright 1997 American Association of Petroleum Geologists