Spatially Variable Sedimentary Thermal Regime of the Continental Shelf off Central Texas Coast

Seiichi Nagihara
Department of Geosciences, Texas Tech University, Lubbock, TX

Bottom-hole temperature data from 133 wells in the continental shelf off central Texas coast have been individually corrected for the disturbance associated with drilling, and yielded 221 estimates for virgin-rock temperatures (VRT) in a depth range of 0.8 to 5.7 km (2600 to 18700 ft) sub-seafloor. Most of the wells are located in the Matagorda Island, Mustang Island, Mustang Island East Addition federal lease areas. The VRT estimates reveal a spatially highly variable geothermal regime. At 4-km (13000-ft) sub-seafloor depth, sedimentary temperatures vary geographically from 110 to 170° C (230 to 338° F) within short distances of a few tens of kilometers. Such variability has not been reported in other parts of the Texas-Louisiana continental shelf. At the high-temperature localities in the northwest corner of the Mustang Island East Addition area, geothermal profiles tend to be of concave-upward shape. The extended period of fast sedimentation in Miocene may have caused recent, shallow sediments to remain relatively cold in contrast to deeper, older sediments which have been fully thermally equilibrated by geothermal heat. It is also possible that hot fluids escaping upward from over-pressured, deeper, older sediments are heating lower Miocene-Oligocene sediments and yielding concave-upward shaped geothermal profiles. The areas of high sedimentary temperatures coincide with the Corsair growth fault trend, and such fluid migration is possible through the faults.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas