Depositional Setting, Structural Style, and Sandstone Distribution in Three Geopressured Geothermal Areas, Texas Gulf Coast

Abstract
Three areas in the Texas Gulf Coastal Plain were studied using electric logs and seismic reflection data to interpret their depositional and structural history and to compare their potential as geopressured-geothermal reservoirs. The Cuero study area, on the lower Wilcox (upper Paleocene) growth-fault trend, is characterized by closely and evenly spaced, subparallel, down-to-the-basin growth faults, relatively small expansion ratios, and minor block rotation. Distributary-channel sandstones in the geopressured lower Wilcox Group of the South Cook fault block appear to be the best geothermal aquifers in the Cuero area. The Blessing study area, on the lower Frio (Oligocene) growth-fault trend, shows wider and more variable fault spacing and much greater expansion ratios and block rotation, particularly during early Frio time. Thick geopressured sandstone aquifers are laterally more extensive in the Blessing area than in the Cuero area. The Pleasant Bayou study area, like the Blessing area, is on the Frio growth-fault trend, and its early structural development was similar; rapid movement of widely spaced faults resulted in large expansion ratios and major block rotation. However, a late-stage pattern of salt uplift and withdrawal complicated the structural style. Thick geopressured lower Frio sandstone aquifers are highly permeable and laterally extensive, as in the Blessing area. In all three areas, geopressured aquifers were created where early, rapid movement along down-to-the-basin growth faults juxtaposed shallow-water sands against older shales, probably deposited in slope environments. Major transgressions followed the deposition of reservoir sands and probably also influenced the hydraulic isolation that allowed the buildup of abnormal pressures. Of the three areas, the Pleasant Bayou area has the best potential for geothermal energy production because of larger fault block area, greater thickness and lateral continuity of individual sandstones, and higher formation temperatures and pressures.
Authors
Charles D. Winker
Robert A. Morton
Tom E. Ewing
D. D. Garcia
Citation

Winker, C. D., Morton, R. A., Ewing, T. E., and Garcia, D. D., 1983, Depositional Setting, Structural Style, and Sandstone Distribution in Three Geopressured Geothermal Areas, Texas Gulf Coast: The University of Texas at Austin, Bureau of Economic Geology, Report of Investigations No. 134, 60 p.

Code
RI134
ISSN
2475-367X
Number
134
Number of figures
49
Number of pages
60
Publisher
The University of Texas at Austin, Bureau of Economic Geology
Series
Report of Investigation
Year
1983