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In the central Texas Gulf Coast, the Eocene lower Wilcox Formation consists predominantly of massive sands updip of the Lower Cretaceous shelf margin. In northeast Fayette County, near the town of Winedale, an inflection point was found at the Lower Cretaceous Edwards and Sligo levels on reconnaissance seismic data. There was a corresponding "wipe-out" of reflectors within the lower Wilcox section above. Prospect-detailing seismic data indicated that the inflection point had localized lateral continuity. A flat spot was mapped at lower Wilcox, Edwards, and Sligo levels.
A well drilled to test the lower Wilcox "wipe-out" zone resulted in a lower Wilcox discovery with initial potential of 2.5 MMCFGD and 50 BCPD. Two delineation wells were dry. The producing sand is near, but not in, the seismic "wipe-out" zone. Genetically indistinguishable from the other lower Wilcox sands, it has a blocky, massive character, decreasing-upward grain size, and is bounded by thin coals. It pinches out updip and is not in the two later wells. An upper delta-plain point-bar depositional model is proposed.
Sands do not correlate well between the wells, but individual coals and groups of coals make excellent correlations. Seismic processing experiments show that resolution of the data improves when high frequencies are retained; in fact, the lower Wilcox "wipe-out" zone disappears.
On the reprocessed seismic data, fairly uniform cycles appear whose boundaries correlate with slightly thicker coals or groups of coals on the well logs. The log interval of each seismic cycle is about 300 ft (90 mi) and includes three or four stacked point-bar sands. An individual point-bar sand, and hence the producing reservoir sand, cannot be resolved on seismic data. It is thought the seismic cycles represent meander-belt cycles, each containing several point-bar sands.
A reprocessed dip line shows that the seismic cycle which includes the producing sand pinches out between the discovery well and the two dry holes. More seismic is necessary to define the lateral limits.
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