Depositional Sequences and Hydrocarbon Exploration in Wilcox Group, South Texas

M. P. Anderson, J. A. Breyer

Five unconformity-bounded depositional sequences are present in the lower and middle Wilcox in south Texas. The sequences are designated A through E, from uppermost to lowermost. Sequences A and B are in the middle Wilcox. Sequences C, D, and E are in the lower Wilcox. Thirty-three gas fields and three oil fields produce from the lower Wilcox in a 1,500 mi² area that includes most of DeWitt County and parts of Gonzales, Karnes, and Lavaca Counties. All but two of the fields are in the Wilcox growth-fault zone. Most of the fields occur in areas with less than 40% sand, downdip from a major sand accumulation. Prospective areas in the growth-fault zone include a strike-trending band across southern DeWitt County in sequence C, an area in central Karnes County and outhwestern DeWitt County in sequence D, and a belt extending from Karnes County into DeWitt County in sequence E. Large areas in DeWitt County and Karnes County updip from the growth-fault zone remain undrilled even though 44 fields produce from the shallow Wilcox immediately along strike to the southwest. The shallow Wilcox trend should be explored in northern DeWitt County and northeastern Karnes County.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.