Analysis of stress change and permeability variations caused by rock failure is of interest in geothermal reservoir development. Cold water injection gives rise to significant pore pressure and temperature changes in the reservoir. These changes need be considered to assess rock failure and permeability change during injection and production process. In this paper, we develop a fully-coupled thermo-poro-mechanical finite element model with damage mechanics and stress dependent permeability. The model takes into account both conductive and convective heat transport. Rock damage is accounted for through alterations of elastic modulus and permeability for the homogenous and inhomogeneous rock mass. The model is applied to the analysis of stress induced micro-seismicity and fracture propagations in geothermal reservoirs. Simulation results for the constant injection rate show effective stress relaxation in the damaged zone and stress concentration at its interface with the undamaged rock. Localized damage propagation in shear and tension are observed for the case of anisotropic in-situ stress. Consideration of rock heterogeneity results in distributed damage and permeability enhancement.

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