In order to advance understandings of the relationships between stress, fracturing, induced seismicity and permeability enhancement, and to provide rich data sets for model improvement and validation, the United States Department of Energy (DOE) Geothermal Technologies Office (GTO) is funding a collaborative investigation of enhanced geothermal systems (EGS) processes at the intermediate-scale (~10-20 m), referred as the EGS Collab project. This project is envisioned to comprise field experiments and the site for the first experiment is on the 4850ft Level below the ground in phyllite of the Precambrian Poorman formation within the Sanford Underground Research Facility (SURF), located at the former Homestake Gold Mine in Lead, South Dakota. Natural fractures of various lengths, orientations, permeability and mechanical cohesive strengths, are abundant within the EGS Collab site. In this study, aimed at interpreting stimulation data and better understanding fracturing behaviors, a series of 2D and 3D simulations using coupled conjugate network flow and quasi-static discrete element model (DEM) are performed. The fracturing behaviors of naturally fractured crystalline rocks under hydraulic stimulations are investigated by systematically varying geometrical, hydraulic and mechanical attributes of natural fractures. Qualitative comparisons with between the simulations and actual stimulation data is performed in this paper to indicate the significance of natural heterogeneities on fracturing patterns and necessities of characterization of natural fractures and induced hydraulic fractures with sufficiently high resolution.

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