Abstract

Exploring for sedimentary geothermal resources on the Gulf Coast of the United States began in the 1970s and the first sedimentary geothermal exploration well, the Pleasant Bayou #2, was drilled just south of Houston, Texas, in 1979. This well successfully proved that geothermal energy could be produced from hot sedimentary aquifers (HSAs) in this basin, however, developing these resources proved to be uneconomic at that time, causing the project to be terminated. At that time, the only way to achieve the necessary flow rates of hot brine to make electricity was to drill vertical wells into Paleocene geopressured-geothermal sandstone reservoirs. Recently, there has been an increase in geothermal exploration in this region, partly because using horizontal wells to target these formations and others can potentially achieve even greater flow rates than at the Pleasant Bayou location.

Five geologic elements represent the main geologic controls on the spatial and temporal distribution of sedimentary geothermal play types on the Texas Gulf Coast. These elements are (1) the location of geopressured reservoirs in Paleogene formations, (2) the location of the Aptian and Albian shelf margins, (3) the type of transitional crust beneath the reservoir, (4) the location of salt diapirs, and (5) the depth to 250°F. Based on these elements, four geothermal areas of interest (AOIs) were identified across Texas. The Sabine Uplift AOI overlies thick transitional crust and 250°F occurs at approximately 9000 ft. The East Texas AOI contains numerous salt diapirs and 250°F occurs around 10,000 ft. The North Houston AOI contains a large geopressured-geothermal zone in the Wilcox formation but 250°F is considerably deeper. The South Texas AOI contains all the key geothermal elements listed above and is consequently optimal for geothermal exploration because multiple sedimentary geothermal play types are near each other.