Geology of Elk City Field: ABSTRACT

Abstract

The Elk City field is in T. 10 N., R. 20-21 W., Washita and Beckham counties, Oklahoma, on the north front of the Wichita Mountains near the axis of the Anadarko basin. The field was discovered by the Shell Oil Company's J. G. Walters well No. 1 in the NE. ¼, SW.¼ of Sec. 14, T. 10 N., R. 21 W., which was completed in November, 1947, from a reservoir at the depth of 9,260-9,360 feet with an initial daily production of 470 barrels, 65.4° A.P.I. gravity condensate, 25 barrels fresh water, and 5,650 MCF of gas. Crude oil was discovered and first produced by the field's second well, the Shell-Long No. 1, NE. ¼, SW. ¼ of Sec. 15, T. 10 N., R. 21 W., which was completed in February, 1949, from a reservoir at a depth of 9,040-9,080 feet, with initial production of 2,345 barrels, 49.1° A.P.I. gravity crude oil, 70 barrels of fresh water, and 3,661 MCF of gas. Subsequently, development has proved several reservoirs in the Missouri series of the Pennsylvanian to be productive of condensate and oil at a depth range from 8,800 to 10,200 feet. The field has a productive extent at present of 7 miles in length and 2 miles in width as determined by about 30 wells producing condensate and crude oil. The probable productive limits have not been indicated along the axis of the field but two dry holes on the north and south flanks, respectively, restrict the probable productive width to less than 3 miles. In the Missouri series of the Pennsylvanian system, this field is structurally an elongate anticline with about 400 feet of closure trending west-northwestward with several culminations along the axis. The initial folding of this structure is unknown due to inadequate knowledge of the deeper strata, but drilling to date has proved that the structure was present during post-Missouri pre-Virgil time. This is shown by angularity at the base of the Virgil series. Further folding probably occurred in Upper Pennsylvanian, Permian, and post-Permian time. The surface beds are Permian in age and extend to a depth of about 6,500 feet. The Pennsylvanian system is composed of more than 7,500 feet of strata extending from 6,500 to below 14,000 feet. The deepest well drilled is the Continental's Proctor No. 1, in the center, NW. ¼ of Sec. 28, T. 10 N., R. 20 W., which penetrated the Pennsylvanian to the depth of 14,572 feet. Although oil and gas showings have been encountered both above and below the Missouri series, the field is presently being exploited from the granite wash and conglomerate reservoirs from 8,800 to 10,200 feet. These reservoir strata are interbedded with shale and marine limestone, but the series is predominantly of a coarse clastic type which ranges lithologically from heterogeneous granite wash to pure quartz sandstone and to limestone conglomerate. Most conceivable combinations of clastic material are present to some degree. One of the more reliable structure markers is a limestone at the top of the Kansas City group located about 500 feet below the top of the Missouri series at a depth of about 8,700 feet. This limestone formation is readily identified from electric logs and is commonly used as a datum for structural interpretation since it immediately overlies the first productive reservoir of the field. Some of the characteristics of the producing reservoirs have been established but more extensive development is necessary to define the total number of reservoirs and their productive extent. All data however show that this is a major field and of importance to the future development of the vast Anadarko basin. Oil and gas recoveries in this field justify the deep drilling necessary and the further exploration for similar accumulations. End_of_Article - Last_Page 626------------