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From December 1987 to March 1991, several operators tested 25 prospects in the lower King sand (Upper Pennsylvanian Cisco Group) play in Concho County, Texas, U.S.A. They used combinations of subsurface geology, reconnaissance airborne gas sensing, surface radiometrics, soil magnetic-susceptibility, and soil-gas hydrocarbon measurements to define prospects. Six new King sand discoveries or extensions and three deeper Goen Limestone discoveries resulted in an estimated exploratory success rate of 36%, and the total exploration and development cost through 1998 was approximately $0.89/bbl of proven producing oil equivalent. Locations for the discovery wells on each of the successful prospects were based primarily on combined subsurface geologic and surface geochemical data.

As detailed examples, we present information on the discovery of Brady Creek and Agaritta fields. The discovery of Agaritta, one of the two largest new-field discoveries, was based on a combination of (1) regional subsurface geologic projection, (2) airborne hydrocarbon sensing, (3) interstitial soil-gas hydrocarbon data, (4) soil magnetic-susceptibility measurements, and (5) surface potassium and uranium concentrations measured by gamma-ray spectrometry.

Also included are surface geochemical data over part of the Lonesome Dove II–Pipe Dream (King sand) field, which clearly demonstrate the complementary nature of anomalies in soil-gas hydrocarbon and soil magnetic-susceptibility measurements.

Subsequent King sand play exploration of the area generally northeast of Agaritta field did not find any further King sand production but did lead to the discovery of the Selden gas field and the New Year ‘95 and Dark Horse oil fields, all producing from the deeper Goen Limestone.

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