Geopressured Geothermal Prospects and Test Well Sites Wilcox Group and Frio Formation, Texas Gulf Coast

Date

1978

Authors

Bebout, Don G.
Gregory, A. R. (Alvin Ray), 1915-
Loucks, R. G.
Weise, Bonnie R.

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Abstract

The four geopressured geothermal prospects and test-well sites described in this report (fig. 1 and table 1) are believed to represent the most favorable locations for testing the resource along the Texas Gulf Coast. The regional and site-specific studies used in selecting the Frio prospects have been published by the Bureau of Economic Geology (Report of Investigations 91); the supporting studies for the Wilcox prospects will be published by mid-1979. Detailed stratigraphic and structural cross sections and net-sandstone and structure maps have been prepared for the fairways in which these prospects are located. It is anticipated that other prospects will be identified in these and other fairways during the course of further study and will be reported on later.

It should be emphasized that these prospects and sites have been chosen on the basis of geology alone and that equally important environmental and legal (surface and mineral rights) aspects have not been considered. The total-resource values shown in the last two columns of Table 1 are very general estimates and are intended only to project an impression as to the magnitude of the resource in these local areas.

A significant departure has been made in the manner in which the top of geopressure is picked in this report. In previous Bureau of Economic Geology reports, the top of geopressure is defined as the point at which the pressure gradient exceeds 0.7 psi/ft; the pressure gradient was determined primarily by plotting drilling-mud weights, a method recognized as highly tentative. For this report, the top of geopressure is picked at the depth at which the plot of the shale resistivity from the electrical log departs from the normal compaction curve. This method is believed to be considerably more reliable.

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