Evaluating the performance of slate geothermal reservoirs using a coupled thermo-hydro-anisotropic mechanical model

This study developed an advanced numerical framework to evaluate the performance of slate-hosted geothermal reservoirs using a coupled thermo-hydro-anisotropic mechanical model. An anisotropic thermo-mechanical failure criterion, established from high-temperature triaxial tests, was integrated into a 3D discrete element method to capture the coupled influences of foliation-controlled anisotropy, injection pressure, and thermal loading during hydraulic stimulation. Benchmark analyses confirmed that the model predictions were consistent with established hydro-mechanical solutions. Additionally, reservoir-scale simulations demonstrated that rock failure and permeability enhancement are highly sensitive to the relative orientation between foliation and fractures. Thermal effects further accelerate degradation along foliation planes, amplifying their mechanical weakness. Among the well-layout scenarios evaluated, horizontal wells oriented perpendicular to the dominant fracture set achieved the highest heat extraction efficiency. Although high injection pressures can increase thermal output, the improvement in thermal output becomes marginal beyond a specific threshold owing to accelerated cooling and earlier thermal breakthrough. These findings highlight the fundamental influence of anisotropy on the efficiency of geothermal-energy extraction and provide valuable insights for optimizing energy-extraction strategies from metamorphic rocks.