EXPLORATION METHODS FOR IDENTIFYING SEDIMENTARY GEOTHERMAL PLAY TYPES IN SOUTH TEXAS

Exploration for geothermal energy resources in sedimentary basins that lack heat flow from crustal extension or active volcanism has garnered much attention in the recent years because of the need for renewable, stable, dispatchable, baseload electricity for residential, commercial, and industrial markets in these regions. The Texas Gulf Coast is a deep basin with high geothermal gradients and a region with a large demand for utility scale electrical power generation and thermal energy for direct use applications. Consequently, identifying geothermal play types in this basin will help to reduce the subsurface risks associated with geothermal exploration and development.

In south Texas, a dataset of 3,407 vertical wells with digital well logs was used to construct a stratigraphic framework for all major formations from the Oligocene Frio Formation to the Oxfordian Smackover Formation for structure mapping. A partially overlapping dataset of 1,867 wells with bottom-hole temperature (BHT) measurements was used to build a series of temperature-depth maps based on corrected bottom-hole temperature measurements across the research area. Combining the temperature-depth maps with the structure maps results in a series of geothermal play fairway maps that shows geographically where each formation intersects different isotherms.

Based on these maps, the Wilcox, Georgetown, Edwards, Glen Rose, Pearsall, and Sligo formations are the shallowest formations across the research area that contain reservoir temperatures capable of electrical power generation (>250⁰ F). Consequently, six different geothermal play types exist within these formation in south Texas: 1) Paleocene and Eocene geopressured-geothermal deltaic and marine sandstones, 2) Aptian and Albian shelf-margin carbonates, 3) Aptian and Albian platform interior carbonate shoals, 4) Maastrichtian deltaic and marine sandstones, 5) salt diapirs and reservoirs of varying age located on the flanks of them, and 6) repurposing existing oil and gas fields within these formations for geothermal energy.