Geologic Setting of the Idaho National Laboratory Geothermal Resource Research Area

Abstract

The Idaho National Laboratory (INL) has designated ~100 km2 of the Eastern Snake River Plain (ESRP), along the track of the Yellowstone Hot Spot, as a Geothermal Resource Research Area (GRRA). The GRRA is a designated area of the INL Site to support research and development for all aspects of geothermal energy. The GRRA is the focus of studies under the Phase I award to the Snake River Geothermal Consortium (SRGC) from the DOE Frontier Observatory Research in Geothermal Energy (FORGE) program. The GRRA provides a robust field site for development of innovative and advanced geothermal technologies, approaches and methods. The GRRA is located in a geological region that is dominated by the Yellowstone volcanic track, the Earth's largest and most active continental hot spot system. It is well known for high regional heat flow (110 mW/m2) and voluminous late Miocene to Holocene magmatism and tectonism. The GRRA is generally underlain by several hundred meters of interbedded Pleistocene basalt lavas erupted from widely scattered vents on the ESRP and sediment derived from mountain ranges northwest of the plain. The basalts and sediments host part of the prolific ESRP aquifer. In the adjacent 3.2 km deep INEL-1 well, these rocks overlie thousands of meters of rhyolites erupted during the climax of hot spot related volcanic activity between ~10 and 4.5 Ma. The rhyolites are dominantly voluminous densely welded ignimbrites, lava flows and shallow intrusions that ponded within and intruded beneath and into coeval caldera systems. Permeability of the thick intracaldera deposits is extremely low due to a combination of very dense welding and rock alteration and mineralization driven by now-extinct intracaldera hydrothermal systems. The extremely low permeability and large mass of the hot deep rocks is ideally suited for EGS studies as heat recovery from this region will require advanced drilling, reservoir stimulation, and fluid injection to achieve necessary heat extraction.