Print this pageThe Utah FORGE Site: A Laboratory for Enhanced Geothermal System Development
Abstract
The U.S. Department of Energy is sponsoring the FORGE (Frontier Observatory for Research in Geothermal Energy) initiative to bring Enhanced Geothermal System (EGS) development to commercial viability and visibility. In contrast with conventional geothermal systems where high-temperature in situ fluids are produced from permeable reservoirs, the EGS concept aims to use petroleum industry hydraulic fracturing technology to create a fracture network in sufficiently hot rock that lacks natural permeability. Water could then be injected into the newly-formed reservoir where it would become heated before being pumped to the surface to generate power. The ability to harness the thermal energy in Enhanced Geothermal Systems could yield more than 100 GWe of cost-competitive generating capacity over the next 40–50 years in the United States alone. The FORGE project will create a controlled environment where technologies and techniques can be tested to create, maintain, and monitor a geothermal reservoir in low permeability granite where temperatures of 175 to 225°C are present at a depth of less than 4 km.
The FORGE site is located in central Utah, 350 km south of Salt Lake City. The area contains numerous renewable energy projects including two conventional geothermal plants, a wind farm, solar arrays, and a biogas plant. Data from more than 100 existing wells and detailed geologic mapping, along with seismic and various other geophysical surveys, have been used to develop a conceptual geologic model of the reservoir. The data show that the temperature and lithologic requirements for the FORGE project can be met over an area of at least 100 km2 and that the total volume of crystalline basement rock with temperatures over 175°C above 4 km depth is more than 100 km3. The MU-ESW1 geothermal exploration well was drilled to a depth of 2.3 km in the summer of 2017 to obtain direct information on the temperatures, permeabilities, rock types, and in situ stresses at the FORGE site. The well encountered temperatures exceeding 175°C in highly fractured, but low permeability granitic rocks. Drill cuttings and two sections of core were analyzed for thermal, lithological, and structural characteristics, and the data confirm the site exceeds all FORGE criteria.
AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018