Geothermal Resources: Frio Formation, South Texas

A preliminary study of the Frio sand distribution and formation temperatures and pressures was undertaken in order to define prospective areas in which a more detailed reservoir analysis is necessary prior to the selection of a site for a geothermal well. As the result of prospective oil wells that penetrated the Tertiary sediments, a geopressured zone containing fluids with high temperatures is known to occur along the Texas Gulf Coast. Few oil or gas wells produce from this area, and the regional sand distribution within these zones is not well known. Limited data, however, indicate that the pore spaces within the sands in the geopressured zone are filled with water which has high temperatures and relatively low dissolved-solids content, and which is saturated with methane. These waters are believed to be an important source of thermal energy and methane gas. For more information concerning the origin of the geopressured zone, see Dorfman and Kehle (1974) and Jones (1970). The first step in appraising the Gulf Coast geothermal resources entails a detailed geologic study of the main sand trends; the Frio and Wilcox Formations appear to be the best prospects. This report will deal largely with the Frio. The Wilcox Formation has been studied by Fisher and McGowen (1967). Other parts of the Tertiary which have been studied in detail are the Queen City Formation (Claiborne), which was reported on by Guevara and Garcia (1972), and the Jackson, reported on by Fisher and others (1970). The United States Atomic Energy Commission, through the Lawrence Livermore Laboratory, and the Center for Energy Studies, The University of Texas at Austin, supported this preliminary study of the geothermal resource of the Frio sands in South Texas. The South Texas area (from just north of Corpus Christi and south to the Rio Grande) was selected because the geopressured zone is known to occur here at shallow depths (Jones, 1970), and because of the abundance of oil well records for the area. The study includes a sand-facies analysis and an integration of the facies data with existing information relative to temperatures and pressures.