Development of Revised Techniques for Assessing Geothermal Resources

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.