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The AAPG/Datapages Combined Publications Database

GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions
Vol. 39 (1989), Pages 231-245

Subsurface Temperature Distributions in South Texas

Deborah S. Pfeiffer (1), John M. Sharp, Jr. (2)

ABSTRACT

Isothermal surfaces and temperature gradients confirm the presence of anomalously high geothermal gradients within south Texas. We have analyzed 2200 oil and gas well logs and compiled more than 5200 corrected bottom-hole temperature measurements. The data show that temperature gradients often steepen from around 1.5°F/100 ft to 3.4°F/100 ft (30°C/km up to 60°C/km) near the top of geopressure (0.7 psi/ft or 15.8 kPa/m) from 6,000 to 12,000 ft (1,830 to 3,660 m) throughout much of the south Texas Gulf Coast. However, the highest gradients coincide with the Wilcox growth-fault zone. Within the Wilcox trend, isotherms indicate that the elevated temperatures become more prominent with depth. Our qualitative analyses indicate that the thermal anomaly is caused by advecting fluids moving upward along and just coastward of the Wilcox fault zone. In addition, preliminary computer modeling indicates that a pulse or pulses of deep upwelling fluids could create the anomalous temperatures. Petrographic and geochemical data are also consistent with enhanced fluid flux in the zones of elevated temperatures, as are the distributions of hydrocarbon and uranium deposits.

Higher temperatures also exist above the top of geopressure along the Wilcox trend. This suggests that fluids are escaping from the geopressured zone via growth faults and perturbing the temperature field in the overlying meteoric regime. Although a few areas of the Vicksburg/Frio growth-fault zones have elevated temperature gradients below the top of geopressure, it is still unknown why such a prominent thermal anomaly occurs along the Wilcox trend but not along the Vicksburg/Frio trends.


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