Office of Renewable Energy Technology Geothermal and Hydropower Technologies Division, FY 1983 Annual Operating Plan

There are between 700 and 3400 guads of recoverable geothermal energy in the US. Hydrothermal, geopressure and hot dry rock are the three principal types of geothermal resources (in order of technological readiness) which can supply large amounts of energy for electric power production and direct heat applications. Hydrothermal resources include water and steam trapped in fractured or porous rocks. A hydrothermal system is classified as either hot-water or vapor-dominated (steam), according to the principal physical state of the fluid. Geopressured resources consist of water at moderately high temperatures at pressures higher than normal hydrostatic pressure. This water contains dissolved methane. Geopressured sources in sedimentary formations along the Texas and Louisiana Gulf Coast are believed to be quite large. Geopressured formations also exist in sedimentary basins elsewhere in the US. Hot dry rock resources consist of relatively unfractured and unusually hot rocks at accessible depths that contain little or no water. To extract usable power from hot dry rock, the rock must be fractured and a confined fluid circulation system created. A heat transfer fluid is introduced, circulated, and withdrawn. The overall goal of the Geothermal Program is to build a technology base that will be used by the private sector to exploit geothermal resources which can supply large amounts of energy for electric power production and direct-heat applications