| Abstract |
According to the estimates from the Department of Energyís (DOE) Energy Information Administration (EIA), the United States faces the need to increase its electrical power generating capacity by 40% (approximately 300,000 Megawatts-electrical or MWe) over the next 20 years. A critical question is the extent to which geothermal resources can contribute to this increasing demand for electricity. The peak installed geothermal power generating capacity of 2860 MWe falls far short of estimated geothermal resources. The reasons for this limited development of geothermal power are varied, involving political, economic and technological factors. In order to better quantify the long-term potential for geothermal energy, the USGS will begin work with DOE, DOE-funded institutions and other state and federal agencies to produce an updated assessment of available geothermal resources in the United States. An important element in updating assessment methodology is the calibration of geothermal resource models with production histories from developed geothermal fields. In the 1970s, USGS assessments applied a volume approach with a constant recovery factor, Rg, of 0.25 as the producible fraction of a reservoirís thermal energy. Analyses of data from fractured reservoirs at The Geysers, Coso and Dixie Valley indicate that Rg is closer to 0.1 and varies depending upon the assumed reservoir size and geometry. Based on these results the volume method remains a simple and accurate approach to quantifying geothermal resources, provided reliable data are available on the size and state of identified geothermal systems. |