Oklahoma City field, Oklahoma County, Oklahoma, is truly a giant oil field. It is a billion-barrel field, having already produced more than that amount of oil and oil-equivalent gas. The Wilcox sandstone alone has produced 50 percent of the estimated 1.07 billion bbl of oil in place. Today the field ranks among the 10 largest oil fields in the United States.

From the very dramatic beginning of the Oklahoma City field 40 years ago, myths have been created from half-remembered tales, but very little of its recent history is known. The purposes of this paper are to update and recount what has happened to Oklahoma City field in the last 36 years and to answer the questions most commonly asked about its origin, growth, size, influence, and destiny.

The field was discovered in 1928 by the drilling of a wildcat well on a 100-ft surface closure. Today the field is 12 mi long and 4 1/2 mi wide. Its 1,000 ft of producing closure is confined in a 32-mi² area and production has come from at least 30 different producing zones.

The discovery well produced from the 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 oil-wet youngest Ordovician Simpson Wilcox sandstone on the lowest part of the west flank of the structure. Production from the Wilcox has been 537.5 million bbl, of which 187.5 bbl of oil was produced by natural gravity drainage.

The field is near the south end of a buried mobile basement feature--the Nemaha ridge--at its intersection with the northeast rim of the Anadarko basin. The structural intersection coincides with an environmentally favorable sedimentary section of thick porous Arbuckle dolomite and alternate sandstone and shale of Simpson Group in a series of shelf-edge hinge zones. In number, variety, and production history, the reservoir beds have not been equaled or surpassed since Oklahoma City's discovery.

The field's structural growth was allied closely with the stages of evolution of the Anadarko basin. Growth probably began in Cambrian time, but surely was in progress from Ordovician through Pennsylvanian time, as a result of subsidence in the Anadarko basin. This subsidence caused compression folding, but the culminating influence on Oklahoma City was a differential vertical displacement in the stronger folds and faulting near the northeast rim of the basin.

The structure was folded, faulted, and truncated contemporaneously. Approximately 2,000 ft of Ordovician-Pennsylvanian strata was removed from the top. A 2,000-ft down-to-the-east fault prevented lateral migration of oil from the fold. The unconformity and the overlying Pennsylvanian shale allowed only limited upward migration. Relief was so prominent, even after truncation and burial, that the fold provided an ideal environment for development and accumulation of oil and gas in the numerous shallow Pennsylvanian zones on its irregular surface. Accumulations within the Pennsylvanian are in pinchouts, fault traps, and channel deposits.

The field has been a model and proving ground for exploration techniques and production technology, modern proration rules and laws, drilling and testing techniques in deep rotary wells, and establishment of standards for formation evaluation and reserve estimates. Developments within a major city furnished excitement caused by many "wild" wells like "wild Mary Sudik," but the field was also an economic benefit during the worst days of the depression. Geologists for the past 40 years have found and developed great quantities of oil and gas in many other areas by using it as a case history for the dating of structural growth as the basis of exploration.