Development of a numerical simulation method for the fluid-mechanical coupled behavior of geothermal reservoir rocks within a fault zone

In this study, numerical simulations considering fault slip due to fluid injection were conducted using the coupled Extended Finite Element Method (X-FEM), which considers flow rate along the fault as well as into rock. A comparison is made between the results from a model that considers the heterogeneous permeabilities, in the fault damage zone, derived from the Discrete Fracture Network (DFN), and a model that uses the equivalent homogeneous permeability, in the damage zone, with the aim of quantifying the influence of fractured fault rocks with anisotropic characteristics. It has been shown that the two models produced the similar magnitude of seismic fault slip, however the heterogeneous permeability model produced the higher maximum seismic fault slip locally, attributed to the higher pressure regions along the fault. This resulted in the seismic to total slip ratio (the average dynamic shear movement divided by the average total shear movement) in the equivalent homogeneous permeability model of 0.27 % and 0.57 % in the heterogeneous permeability model. Interestingly, the seismic fault slip mainly produced on the edge of the pressurized zone in both models, which aligns well with field observations. These results imply the applicability of this coupled X-FEM approach to predict fault slip due to fluid injection and indicate a certain degree of influence of the damage zone with anisotropic characteristic on fluid-induced fault slip.