Thermal Gradients in the Texas Continental Shelf

Seiichi Nagihara¹ and Michael A. Smith^2
1 Department of Geosciences, Texas Tech University, Lubbock, Texas 79409-1053
² Minerals Management Service, New Orleans, Louisiana 70123-2394

Bottom-hole temperature data from 98 wellbores on the Texas shelf were corrected for the effects of drilling, such as circulation of drilling fluids, and yielded 190 virgin rock temperature estimates from sediment lying between depths of approximately 0.6 to 3.7 mi (1 to 6 km) below the sea floor. Geothermal gradients at 13 locations obtained from this data, were spatially interpolated to yield a regional overview for the geopressured Texas shelf. Average observed thermal gradient values (0.011 to 0.022°F/ft or 0.02 to 0.04 K/m) were greater than those of offshore Louisiana and eastward (0.008 to 0.016° F/ft or 0.015 to 0.03 K/m) and appeared to decrease basinward. The variance towards lower thermal gradients appears to have been driven by the massive, Cenozoic, deltaic influx causing sedimentary particles to be buried deeply with less heating. This occurred more prevalently off the Louisiana coast around depocenters, and as these depocenters migrated further offshore, more recent sediments accumulated on the outer shelf resulting in even lower thermal gradients. However, a portion of the Mustang Island shelf area does not reflect the lower thermal gradient trend, but instead, shows an anomalously high thermal gradient (0.031°F/ft or 0.057 K/m). There are two possible explanations for this anomaly. First, there may be a steady flow of hot geopressured fluids migrating up fault pathways. Second, the heat flow locally released from the igneous basement may be greater than in the surrounding areas.

AAPG Search and Discover Article #90069©2007 GCAGS 57th Annual Convention, Corpus Christi, Texas