Distribution of Abnormal Pressure in Lower Vicksburg, Hinde Field, South Texas

Kirk A. Barrell

Hinde field is located downdip from the Vicksburg fault zone in an area of abundant gas production. The gas is produced from abnormally pressured sandstones. The local structure consists of a major listric normal fault that acts as a detachment surface on top of the Jackson shale. Rollover closure is present, with 600 ft of reversal at approximately 9,500 ft. The Vicksburg Formation consists of thick wedges of sand separated by marine shales. Cumulative field gas production as of January, 1987 was 19 bcf.

Three distinct zones of abnormal pressure are present. The first occurs in the Frio section at depths of 4,000-5,600 ft. The second and third zones occur in the Vicksburg section at depths of 6,400-7,500 ft and 8,300-10,000 ft, respectively. These zones of abnormal pressure are evident on conductivity plots where the observed conductivity deviates from the normal decrease with depth. They are separated by zones in which the pressure returns to hydrostatic. Apparent pressure gradients range from 0.69 to 0.83 psi/ft with an average of 0.76 psi/ft, and gradients increase with depth. The T. B. Slick 66, the discovery well, had an initial bottom-hole pressure of 8,400 psi with a gradient of 0.80 psi/ft. Flow probably exists from the lower Vicksburg downward to the fault plane and upward fr m the underlying, overpressured Jackson shale. However, flow in the upper Vicksburg is probably up to the basal Frio sandstones. Abnormal pressures are probably released by flow along minor faults.

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