Influence of permeability anisotropy on rock damage and heat transfer in geothermal reservoir

Enhanced geothermal system technology is in the focus of geothermal energy research due to its large economic growth potential. This study illustrates a pseudo-3D doublet model of EGS using coupled thermo-hydro-mechanical-damage modeling processes in the framework of TOUGHREACT-FLAC3D. Three cases were simulated to evaluate the effect of anisotropic permeability (η=5, 1, 0.2) on conducting damage, inducing permeability evolution, reducing elastic module, changing reservoir pressure, and thermal power output. The results show that the overall damage zone decreases with the enhancement of anisotropic permeability ratio η, for η=5, the damage zone increases with time, and the damage breakthrough appears earlier than the other cases. The fracture permeability of model is obviously affected by the evolution of rock damage and the degradation of elastic modulus, which is the main reason to induce rock damage. The injection-production pressure difference is another factor to rock damage except for thermal stress, which becomes the dominated factor as the model with a lower value of η, and injection-production pressure difference may be more influential to the model with low anisotropic permeability η. There is a threshold of permeability anisotropy ratio to balance the above two factors. Comparing the performance of thermal power output in various cases, the increasing reservoir permeability can be controlled to favorable for increasing the efficiency and production of thermal in a short time. From the perspective of whole reservoir lifetime, the effect of injection-production pressure difference on increasing the thermal production is more evident.