The paper presents results of a micro-mechanical Discrete Element Method (DEM) study of the hydraulic fracture initiation and propagation in Enhanced Geothermal System (EGS) performed using the Particle Flow Code (PFC). Hydraulic fracturing is the main means to stimulate and create flow paths to extract heat in hot dry rocks with insufficient permeability to inject and circulate fluids. Hydro-thermo-mechanical coupled modeling is performed to analyze stress and strain changes on fracturing from a wellbore for improving the understanding of the role of thermal stresses on fracture propagation processes and the resulting fracture geometry. Bonded particle model (BPM) that is used for modeling the mechanical response and fracturing of solids was modified for capturing mechanical effects of temperature difference between rock and fracturing fluid infiltration in the propagating fracture. Heat exchange between fluid and rock and fracture is fully coupled processes. As the fracture propagates from the pressurized borehole, both fluid and rock adjacent to a newly formed fracture change temperature. The results show that thermally induced stresses can significantly change the fracture initiation and the fracture propagation pattern. Thermal stresses cause shallow randomly oriented cracks. The study evaluated fracture geometry and orientation with respect to fracturing fluid temperature, viscosity, density, pressure, rock parameters and in-situ stress difference.
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