Jack Hunter Norbeck, Timothy Latimer

Fervo Energy has completed construction of a commercial enhanced geothermal system (EGS) project and has qualified full functionality of the system through production testing at commercially relevant operating conditions. The project site is located in a nearfield setting adjacent to an operating geothermal power station in north-central Nevada and is designed to deliver an uplift in high-temperature geothermal flow rates to increase the power capacity at the facility.

The project involved drilling a first-of-a-kind EGS horizontal doublet well system, consisting of an injection and production well pair within a high-temperature, hard rock geothermal formation. The lithology of the target reservoir is characterized as a mixed metasedimentary and igneous formation, comprised of phyllite, quartzite, diorite, and granodiorite, representative of the geology across the most prospective geothermal areas throughout the western US. The lateral sections of the wells were drilled with 9 7/8" hole size, completed with 7" casing, extended approximately 3,250 ft horizontally, and reached a maximum measured temperature of 376 $^\circ$F. A modern multistage, plug-and-perforate stimulation treatment design with proppant was used to enhance the permeability of both horizontal wells. A 37-day crossflow production test was performed in April-May 2023, confirming that the EGS wells are connected hydraulically by a highly conductive fracture network. During production testing, the system achieved flow rates of up to 63 L/s, production temperatures of up to 336 $^\circ$F and a peak power production of 3.5 MW electric power equivalent. Flow profile wireline logs were performed on the horizontal injection well during the crossflow test, validating that the stimulation treatment design resulted in flow allocation along the entire lateral. Production temperature increased continuously throughout the test, indicating that no significant thermal short-circuit pathways were created during stimulation operations.

Based on a review of historic EGS projects, Fervo's horizontal doublet well design is most productive EGS system to-date in terms of flow rate and electric power equivalent. In successfully completing this project, we have demonstrated that no major technical barriers exist to deploying horizontal EGS systems in similar metasedimentary or igneous formations up to temperatures of approximately 400 $^\circ$F. Numerical reservoir simulation models calibrated with the field data from this project demonstrate a clear innovation pathway to increasing the power capacity up to 8 MW of electric power per production well, meeting or exceeding the performance criteria outlined in Advanced Scenario the National Renewable Energy Laboratory's 2023 Annual Technology Bulletin for geothermal energy.