Three-dimensional quasi-static discrete element modeling of hydraulic fracture propagation in crystalline rock under thermal-mechanical stress gradient

Aimed at supporting the hydraulic fracturing experiments in EGS Collab project, a three-dimensional (3D) quasi-static discrete element model (DEM) incorporating hydro-thermo-mechanical (HTM) coupling effects has been developed and applied to simulate the hydraulic fracture propagation under the influence of stress alterations due to the drift evacuation and its longer-term cooling effects. The induced stresses are modeled by developing a 3D quasi-static DEM model and validated against that from commercial finite element model package. It is observed that the fracture starts from a more-or-less penny-shaped crack and then becomes less symmetric with a preferred growth direction toward the drift which the stress nearby is less compressive. Sensitivity studies are then performed to understand how the operational parameters, such as injection rate, impact the fracture size, geometry and aperture distribution. The containment mechanism of propagating fracture by production wells is also investigated, and the simulation results clearly indicate the risk of hydraulic fracture intersecting the drift is minimum when producing wells exist in the neighborhood.