Numerical insight into performance of enhanced geothermal system under the influence of rock matrix anisotropy

• A THM coupling model for anisotropic EGS was established. • Anisotropic models have higher initial heat extraction rate (33 MW). • Temperature in anisotropic model is 5°C higher than isotropic ones for days. • Velocity in anisotropic cases is higher, enhancing overall seepage capacity. The mechanical properties and permeability of hot dry rock (HDR) reservoirs exhibit directional variations, which significantly influence fluid flow and heat transfer in Enhanced Geothermal Systems (EGS). However, current studies seldom account for the mechanical and seepage anisotropy of the reservoir matrix, which may result in significant discrepancies between numerical simulations and actual field performance. This study develops a thermo-hydro-mechanical (THM) coupling model that incorporates anisotropy in HDR fractured reservoirs, solved using the Finite Element Method (FEM), and compares the heat transfer characteristics of anisotropic and isotropic reservoirs. The results show that mechanical anisotropy alters the distribution and range of stress concentration zones (e.g., 300 MPa maximum stress near injection wells in both cases, but a 15% larger concentration area in anisotropic reservoirs) without affecting the final displacement field. Anisotropic reservoirs exhibit an initial heat extraction rate of 33 MW, 37.5% higher than isotropic counterparts (24 MW). This advantage persists for 500–5500 days, with production well temperatures remaining 5°C higher than those of isotropic reservoirs. After 20 years of operation, anisotropic reservoirs show a lower average temperature (90.74°C vs. 97.45°C), indicating enhanced heat transfer efficiency. The matrix flow velocity in anisotropic cases is 2.1 times higher than that in isotropic cases, significantly improving seepage capacity. Permeability anisotropy induces directional fluid migration, with pressure fronts propagating 18% faster in the high-permeability direction (aligned with fracture orientations). These findings confirm that reservoir anisotropy significantly impacts EGS heat transfer performance and cannot be ignored, providing quantitative guidance for optimizing fracture network design and well placement in engineering practice.