In the central Texas Gulf Coast, the late Paleocene-Eocene lower Wilcox Formation consists predominantly of massive sandstones updip of the Lower Cretaceous shelf margin. An exception is in northern Lavaca County where the lower Wilcox was incised by submarine canyons (e.g., the Yoakum shale channel) during middle Wilcox deposition. Productive sandstones in Valentine field and other nearby fields are remnants of the lower Wilcox between, and in places below, these shale-filled canyons.

Regional speculative seismic data were examined northeast of the anomalous Lavaca County area to find analogous geologic conditions in unleased acreage. In northeast Fayette County, near Winedale, terracing was found at the Lower Cretaceous Edwards and Sligo levels, with a corresponding wipeout of reflectors within the lower Wilcox above the terracing. Seismic data indicated that the terracing had localized lateral continuity. A flat spot, mapped at lower Wilcox, Edwards, and Sligo levels, was found to influence even the surface topography. When regional dip was removed, the present-day flat spot became a closed structure.

A well drilled to test the lower Wilcox reflection wipeout zone resulted in a discovery with an initial potential of 2.5 MMCFGD and 50 BCPD. Sidewall cores of the high-resistivity spikes bounding the producing sand encountered lignitic coals. A synthetic seismogram of the producing well showed that the top of the lower Wilcox, as picked on the regional seismic data, correlated to the uppermost coal. Because the discovery well had a water contact, two delineation wells were drilled updip. These wells were 5,000 ft apart, and each was about 3,000 ft from the discovery well. The producing sandstone pinched out, and both offset wells were dry holes.

The massive, lower Wilcox sandstones did not correlate well between the three wells, but individual coals and groups of coals made excellent correlations. Seismic data showed that the lower Wilcox was composed of a series of cycles, and cycle boundaries correlated with slightly thicker coals or groups of coals of widespread areal extent. Within the producing-sand seismic cycle, strong pinch-outs were seen on the strike and dip seismic lines near the producing well, as well as within other seismic cycles. However, a three-dimensional program is needed to trace the pinch-outs within various seismic cycles across the Winedale structure.

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