ABSTRACT: Hydraulic stimulation to reactivate and shear-dilate fractures can successfully enhance the permeability of geothermal reservoirs sufficiently to obtain commercial flow rates. The process involves strongly coupled physical processes, including reactivation and deformation of fractures, deformation of surrounding rock, and fluid flow in the fractures and their surroundings. In this paper, we present some improvements to a previous numerical modeling approach. The basic conceptual model of the reservoir is based on representing fractures as two-dimensional surfaces with associated apertures in a three-dimensional domain. Considering both flow and deformation, processes in the fractures are coupled with processes in the surrounding host rock. Flow is assumed to be governed by Darcy’s law both in the fractures and the matrix. Fracture reactivation is based on a Mohr-Coulomb criterion, and the corresponding irreversible deformation is based on static-dynamic friction law. For the rock surrounding the matrix, we assume linear elastic deformation to model the response of the formation to shear-dilation of the fractures. Numerical results show how the methodology can be applied to understand important mechanisms affecting permeability enhancement. The possibility to model well response and induced seismicity in a hydraulic stimulation process can potentially aid the analysis of field observation data.

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