Hot, Dry Rock (HDR) geothermal energy: exploitation and exploration

The Los Alamos Scientific Laboratory (LASL) method of extracting geothermal energy from HDR requires two drill holes connected at depth by a large, vertical, hydraulic fracture. Water, introduced through one drill hole, is heated as it passes along the fracture toward the second drill hole, through which it is returned to the surface. This method of energy extraction is being tested at Fenton Hill near the Valles Caldera in north-central New Mexico where suitable reservoir conditions have been demonstrated (200/sup 0/C, essentially impermeable rock) at a depth of 3 km. With continuing success in developing the extraction technique and characterizing the first proven HDR site, it is now appropriate to examine and evaluate exploration techniques for this type of geothermal deposit. Geologic, geochemical, and geophysical techniques have been used to identify and characterize the HDR part of the total geothermal system related to the Valles Caldera. As is usual in exploration, a combination of techniques has proved most useful. Geologic mapping, geochronology, and heat-flow measurements were used to evaluate the nature, age, and magnitude of the heat source. A variety of geologic and geophysical techniques provided information on the permeability of the potential reservoir. Much of the information gained andmore » tested by drilling at Fenton Hill now can be applied to the search for other HDR sites.« less