Subsurface Temperature Distributions in South Texas

Deborah S. Pfeiffer, John M. Sharp, Jr.

Isothermal surfaces and temperature gradients confirm the presence of anomalously high geothermal gradients within south Texas. We have analyzed over 2,200 oil and gas well logs and compiled more than 5,200 corrected bottom-hole temperature measurements. The data show that temperature gradients often steepen from around 30°C/km up to 60°C/km near the top of geopressure (> 15.8 kPa/m from 1,800 to 3,600 m) through 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 he 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, which 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 and Frio trends.

AAPG Search and Discovery Article #91029©1989 AAPG GCAGS and GC Section of SEPM Meeting, October 25-27, 1989, Corpus Christi, Texas.