Enhanced geothermal system potential for sites on the eastern Snake River Plain, Idaho

The geologic characteristics and evolution of the Eastern Snake River Plain are consistent with transfer of large amounts of magma advected heat at mid- to upper-crustal levels. We speculate that some of this heat is stored below surficial basalt lavas, within underlying dense, hydrothermally altered rhyolites that infill large nested calderas. Cryptic hydrothermal systems may occur within caldera-related fracture systems, or megabreccias near caldera collapse scarps. Blind hot zones are also possible below young chemically evolved volcanoes on the ESRP. Other factors in addition to high temperatures and high heat flow that support EGS development are also prevalent on the ESRP. A number of deep exploration wells exist, and hundreds groundwater wells provide additional information on the character and makeup of the subsurface. The abundant cold groundwater resource can provide a significant heat sink for power generation, and also provide working fluid and makeup water as necessary. Regional stress and earthquake data suggest that the Plain is extensional to isotropic and "quiet". The seismic risks of the eastern Snake River Plain have been extensively investigated because of the nuclear facilities at Idaho National Laboratory. The epicenter of the 1983 (magnitude 7.3) Borah earthquake was located about 100km (70 miles) from INL's nuclear facilities, but no significant damage occurred. This is attributed to the alternating layers of hard basalt and soft sediment that lie beneath the Snake River Plain. This attenuation reduces the seismic risk from natural and induced seismic occurrences. Additional studies are currently underway to better understand the EGS potential for the eastern SRP. These include GIS and VSRP analysis of existing data, new geotechnical and geomechanical analysis of core samples, geochemical studies of water-rock interaction, and numerical modeling studies of fracturing, fluid flow, and heat recovery.