Heat variations caused by groundwater flow in growth faults of the South Texas Gulf Coast Basin

Zones of above average subsurface temperatures have been noted in certain areas of the Gulf Coast basin. Their cause has often been credited to geopressure, which presumably traps heat because of higher porosity and consequently lower thermal conductivity. I determined the temperature distribution in a portion of South Texas by collecting and analyzing over 1600 bottom-hole temperature measurements. The analysis included correcting the temperatures with the Kehle correction scheme, constructing isothermal surfaces by both interpolating and extrapolating the data, and Kriging the result. Temperature profiles were plotted for twelve subregions of the study area. The greatest temperature anomalies are associated with the Tertiary Wilcox growth fault zone, and the simple presence of geopressure is insufficient to account for the temperature anomaly. Numerical modeling indicates that growth faults act as zones for concentrated vertical flow. The upwelling of deep basinal fluids advects heat and causes the high temperatures observed in the growth fault zone. The model, by Smith (1983), is two-dimensional, finite element, steady state, and couples heat and fluid transport. It indicates that the source of these fluids is deep, perhaps over 20,000 feet (6096 m) below the surface. The modeling results also suggest that an unidentified region of high thermal and hydraulic conductivity could exist coastward of the Wilcox faults at a depth of about 15,000-20,000 feet (4572-6096m).