Elevated Sediment Temperatures along Growth Faults in the Texas Continental Shelf

Four near-parallel, growth fault systems dissect sediments of the continental shelf off the Texas Gulf Coast. They are named “Lunker”, “Clemente-Tomas”, “Corsair”, and “Wanda” from the inner to the outer shelf. The Corsair and Wanda systems reach deep (10- to 12-km depths) into Mesozoic sediments, while the other two terminate in much shallower Tertiary sediments. Previous reservoir fluid analyses performed for a gas field along the Corsair system suggested that deep-cutting faults there act as the conduits for upward migration of fluids expelled from Mesozoic sediments. The advective heat transport by such fluid flow may elevate the temperature in the faulted sediment, while flow is active. The present study examined bottom-hole temperature (BHT) data reported from wells drilled in the Brazos, Matagorda Island, and Mustang Island federal lease areas in the Texas shelf, which include the outer three of the aforementioned growth fault systems. The BHTs were individually corrected for drilling-related thermal disturbances (Horner plot method) and yielded 310 estimates of pre-drilling formation temperatures from 183 wells. The corrected BHTs were spatially interpolated to yield a series of temperature distribution maps in a depth range of 3 to 5-km below seafloor. Even though there are some wide gaps in the geographic coverage of the data, the maps show higher sediment temperatures along the Corsair and Wanda systems in the outer shelf. The zones of high temperatures are not geographically continuous throughout these fault systems, however. Upward migration of hot fluid along the deep-cutting faults at some localities along the Corsair and Wanda systems may explain the observed thermal regime, but the effects of other factors such as the presence of salt in the outer shelf and the sediment displacement resulted from the faulting should also be considered.