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Gravity, magnetic, and seismic surveys combined with subsurface geologic investigations resulted in very intriguing interpretations of an area east of Crystal City, Texas. The study area includes the south-central part of Zavala County east of the Nueces River and the adjoining parts of Dimmit County to the south. The Elaine field is included in the study area.
Gravity and magnetic residuals were calculated using the least-squares method, and the magnetic surveys revealed several serpentine plugs, which are confirmed by seismic interpretations. Although no geophysics work was done, subsurface study shows that Elaine field is the largest of these plugs. Seismic studies also show that the Austin Chalk, on whose surface the lava was extruded, is highly fractured and faulted. The Austin under the Elaine field is the lowest structural feature in the area.
The Anacacho was deposited on the lava surface, and in the Elaine area it has a reeflike appearance. Isopachs of younger sediments show that they are draped and differentially compacted over the plugs, and that the Elaine plug affects sediments as young as Escondido.
Production in the area is mainly from the San Miguel, but significant amounts of hydrocarbons have also been produced from Eagle Ford, Austin, Anacacho, and Olmos reservoirs.
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