Temperature Dependence of the Poroelastic Properties of Utah FORGE Granitoids - Part I

ABSTRACT: Coupled thermo-poromechanical processes are important in geothermal systems development. While poroelastic properties are typically measured at room temperature, it is essential to evaluate them under actual reservoir conditions to capture their true behavior. We conducted extensive poroelastic tests on Utah FORGE granitoids across a temperature range of 25-190°C. The results indicate that these samples exhibit varied responses to increased temperatures, some undergo thermal strengthening, others experience thermal weakening, and some remain relatively insensitive to temperature changes. Despite these differences, all samples show a decline in permeability with increasing temperature, though the extent of permeability reduction varies. Drained bulk moduli generally increase with temperature and, for some samples, become less sensitive to effective stress due to the closure of micro-fissures upon heating. Consequently, Biot's coefficients exhibit different characteristics at room temperature and elevated temperatures, showing strong stress dependence on temperature. This suggests that Biot's coefficient values measured at room temperature condition cannot be simply extrapolated to high-temperature regimes. The underlying mechanisms governing permeability changes and the thermal strengthening or weakening effects observed in these granitoids are further explored, providing critical insights into their thermo-poroelastic behavior and implications for geothermal reservoir performance. This paper presents Biot's coefficients and permeabilities for tests conducted under drained conditions, while a subsequent paper, Part II of this series, will report Skempton's B and thermal pressurization coefficients for tests conducted under undrained conditions.