High-Temperature Triaxial Direct Shear Testing for Utah FORGE

Abstract

Measurements of the coupled thermo-hydro-mechanical-chemical (THMC) properties of rock fractures are sparse, and even more so at high-temperature. The Utah Frontier Observatory for Research in Geothermal Energy (FORGE) has a reservoir temperature near 200 °C, hydrostatic pressure exceeding 20 MPa, and minimum principal stress exceeding 35 MPa. Here, we present the results of our laboratory experiments to measure the THMC properties of shear fractures that are created and slip-stimulated at FORGE site conditions. Our rock samples are granite and gneiss specimens taken from well 16A(78)-32. Our methodology is triaxial direct-shear with high-temperature. Injected fluids mimic the chemistry of a previously planned injectate, sourced from a nearby golf course. Using intact samples, our results provide measurements for the shear strength, dilation, permeability, hydraulic aperture, stress-dependent aperture, and effluent chemistry. This information provides data for modeling the FORGE site, and for other sites having a similar geologic setting.