1. References Bebout, D.G., Loucks, R.G., Gregory, A.R., Report of Investigations No. 91: Frio Sandstone Reservoirs in the Deep Subsurface Along the Texas Gulf Coast: Their Potential for Production of Geopressured Geothermal Energy. Bureau of Economic Geology, University of Texas at Austin, Austin Texas, 1978. Bebout, D.G., Weise, B.R., Gregory, A.R., Edwards, M.B., Wilcox Sandstone Reservoirs in the Deep Subsurface Along the Texas Gulf Coast – Their Potential for the Production of Geothermal Energy, Bureau of Economic Geology, University of Texas at Austin, Austin, Texas, 1982. Blackwell, D.D., Negraru, P.T., and Richards, M.C., Assessment of the Enhanced Geothermal System Resource Base of the United States, Natural Resources Research, DOI: 10.1007/s11053-007-9028-7, 2007. Campbell, R. G., and Hattar, M. M., Operating results from a hybrid cycle power plant on a geopressured well, Geothermal Resources Council Trans., 14, 521-530, 1990. Campbell, Richard G.; Hatter, Mai M.. Design and Operation of a Geopressured-Geothermal Hybrid Cycle Power Plant: Final – Volume I – February 1991. The Ben Holt Co.; Pasadena, California, 1991. Campbell, R.G., Hatter, M.M., Design and Operation of a Geopressured-Geothermal Hybrid Cycle Power Plant: Final Report – Volume II – February 1991. The Ben Holt Co.; Pasadena, California, 1991. John, C.J., Maciasz, G., Harder, B.J., Gulf Coast Geopressured – Geothermal Program Summary Report Compilation: Volume I – Executive Summary. Basin Research Institute, Louisiana State University. Baton Rouge, Louisiana, 1998. Fairways WilcoxFrio Miocene-Pleistocene Armstrong Fairway thick sand moderate temperature permeability unknown Hidalgo Fairway thick sand high temperature low permeability Corpus Christi thin sand high temperature low permeability Matagorda Fairway thin sand limited aerial distribution high temperature high permeability Brazoria Fairway thick sand high temperature high permeability Hidalgo & Armstrong Fairways 200°F 300°F Top of geopressure Corpus Christi & Matagorda Fairways 200°F 300°F Top of geopressure 200°F 300°F Reservoir Salt withdrawal basin Reservoir 0 25 50 miles Brazoria Fairway -98-94-92-90-96 26 28 30 32 DOE Test wells From the mid 1970’s to the early 1990’s the DOE sponsored geopressure research on wells in the Gulf Coast. Sixteen wells were chosen and divided into two programs, Wells of Opportunity and Design Wells. The Wells of Opportunity focused on wells provided by the oil and gas industry where geopressured reservoirs were penetrated. Design wells were placed where geologic and geophysical data indicated best conditions for a geopressure prospect. Data gathered include subsurface structure, regional sandstone distribution, porosity permeability, temperature, formation pressure and salinity. Temperature at Depth These temperature models were calculated quantitatively using the following relation: where T(x) is the temperature at depth x, Q0 is the surface heat flow, K is the average thermal conductivity from the surface to depth x, and A0 is the radioactive heat contribution from crustal rocks. Target temperatures (in pink) in the geopressured fairways are reached as shallow as 4 km. The Texas and Louisiana Gulf Coast region of the US holds vast reserves of potential energy. This energy falls into the category of geopressured water resources. As the name implies, the water at depth is over pressured and therefore flows to the surface under its own power. This water carries with it two important sources of energy, natural gas and geothermal heat. Both can be separated from the water and processed into usable energy allowing the water to be reinjected back into the earth. From 1975 to 1988 the US Department of Energy spent millions of dollars for data compilation and reports outlining potential geopressure prospects. These reports include, but are not limited to, temperature at depth, geochemistry and geologic structure. The data come from the multitude of wells along the Gulf Coast. The reports culminated in outlining what are called geopressured "fairways." These fairways are areas in which several factors overlap. First, the underlying formations must have large bodies of high porosity sands and therefore large volumes of water. This water has to be overpressured thereby giving it a greater thermal gradient. This provides higher temperature water at a shallower depth. These areas of overlapping characteristics, or "fairways", are places where favorable conditions exist for geothermal energy to be produced. Poster by: Patrick R. Stepp Southern Methodist University Frio Sands These two figures show reservoirs located in the Frio sandstone formation. The red dashed lines are 200° and 300°F isotherms, while the blue lines represent the top of the geopressure. This figure as well as the report itself outlines in detail each of the fairway’s positive and negative aspects. In the past, the cutoff temperature has been the 300°F isotherm, today’s standard of 230°F is lower and encompasses larger volume. (Bebout et. al 1978) (John et. al 1998) Pleasant Bayou Power Plant DOE with the Ben Holt Company began operating the Pleasant Bayou Power Plant, located in Brazoria, Texas, in 1989. The 1 MW plant produced 39.2 MMscf of methane gas and 1.4 MMstb of hot brine to produced 3,445 MWh of electricity running at 98% capacity during its operational run from November 1989 to May 1990.