Competition between thermoelastic process and mineral reaction on fracture flow channeling

Abstract

Fracture flow channeling stemming from heterogeneous aperture distribution is a widely observed phenomenon in enhanced geothermal systems (EGSs) and has been considered a main cause of unsatisfying thermal extraction performance. Many numerical studies have been performed to quantify the impact of flow channeling on thermal performance, while the dynamic evolution of flow channeling under complex thermo-hydro-mechanical-chemical (THMC) coupled processes remains underexplored. This study develops a 3D field-scale THMC coupled EGS model with heterogeneous fracture apertures to systematically investigate the individual and joint effects of thermoelastic process and mineral reaction on fracture flow channeling and long-term thermal performance. The results demonstrate that during long-term injection of undersaturated water, the thermoelastic process leads to aperture enlargement in low-temperature zones, intensifying flow channeling, whereas the mineral dissolution preferentially enlarges fracture aperture in high-temperature zones, leading to flow dispersion. These two mechanisms exhibit strong physicochemical feedbacks: the mineral dissolution counteracts thermoelastic-induced flow channeling by enlarging heat exchange zones and homogenizing thermal stress distributions, while the thermoelastic process enhances the effect of mineral dissolution by narrowing heat exchange zones. Parametric analyses further reveal that reservoirs with higher rock elastic modulus and lower fracture stiffness are more susceptible to severe thermoelastic-induced flow channeling, whereas higher injection temperatures, lower injection concentrations, and greater reactive mineral content enhance the mitigating effect of mineral dissolution. These findings suggest that long-term thermal performance of EGSs can be optimized by selecting reservoirs with low elastic modulus, high fracture stiffness, and abundant reactive minerals, combined with high-temperature, undersaturated injection strategies.