1978 USGS Geothermal Resource Assessment

Abstract

Geothermal resource assessment can be defined as the broadly based estimation of supplies of geothermal energy that might become available for use, given reasonable assumptions about technology, economics, governmental policy, and environmental constraints (Muffler and Christiansen, 1978). This assessment implies not merely the determination of how geothermal energy is distributed in the upper part of the earth's crust but also the evaluation of how much of this energy could be extracted for man's use. energy in place in the earth's crust (relative to a reference temperature) is the geothermal resource base. The accessible resource base is the thermal energy at depths shallow enough to be tapped by drilling in the foreseeable future (Muffler and Cataldi, 1978). That fraction of the accessible resource base that could be extracted economically and legally at some reasonable future time is the geothermal resource (Muffler, 1973; White and Williams, 1975; Muffler and Cataldi, 1978). This geothermal resource contains both identified and undiscovered components. Finally, the geothermal reserve is identified geothermal energy that can be extracted legally today at a cost competitive with other energy sources. The relationships between these terms can be illustrated on a McKelvey diagram for geothermal resources (figure 1).