Current Activities At The Utah Frontier Observatory For Research In Geothermal Energy (forge): A Laboratory For Characterizing, Creating and Sustaining Enhanced Geothermal Systems

The U.S. Department of Energy’s (U.S. DOE) Frontier Observatory for Research in Geothermal Energy (FORGE) is a field laboratory where tools and technologies required for creating, sustaining, and managing Enhanced Geothermal Systems (EGS) can be tested under reservoir conditions. This paper provides an update of activities occurring at the Utah FORGE site in south-central Utah.

Since 2016, six wells have been drilled. Five of the wells, 56-32 (9,145 ft), 58-32 (7,536 ft), 68-32 (1,000 ft), 78-32 (3,289 ft), and 78B-32 (9,500 ft) are vertical and will be used for microseismic monitoring and tool testing. The sixth well, 16A(78)-32, will serve as the injection well for reservoir creation and circulation. Well 16A(78)-32 was drilled vertically to 5,892 ft, deviated 65° from vertical, before reaching a total depth of 10,987 feet MD and a true vertical depth of 8,561 ft. The well recorded a temperature of 427oF.

All of the wells encountered similar lithologies. With depth, the wells penetrated granitic alluvium above the basement rocks consisting of a Tertiary rhyolite dike, Tertiary plutonic rocks ranging in composition from granite to monzodiorite, and in the deepest wells, interfingering granite and Precambrian metamorphic rocks. The contact with the rhyolite and alluvium dips west at ~25o. This contact is interpreted to be a rotated and eroded Basin and Range bounding fault.

Injection tests have been conducted in 58-32 and 16A(78)-32. A short-term stimulation test to measure stress in the open hole section of well 16A(32)-78 was conducted shortly after the well was completed. The results indicate a closure stress gradient of 0.71-0.75 psi/ft and very low permeability of ~30 micro-Darcies.

Additional stimulations of 16A(78)-32 will be conducted in April 2022. The stimulation will consist of three stages near the toe of well; two in the basement rocks behind casing and one in the open hole section of the well. Drilling of the production well and reservoir creation is planned for late 2022.

Regional microseismicity has been monitored since 1981, but no events have been detected below the Utah FORGE site. The seismic monitoring network consists of two concentric rings of permanent borehole and surface seismometers, fiber optic cables and geophone strings in the three deep vertical wells . This network will remain in place throughout the project’s life. During stimulations, the network will be augmented with nodal arrays and surface fiber optic cables.

All data, including injection testing results, microseismic data, geophysical and image logs, cuttings, and core samples are in the public domain. The data can be accessed through the Geothermal Data Repository.