Simulated Evolution of Fractures and Fracture Networks Subject to Thermal Cooling and Fluid Pressure Changes: A Coupled Network Flow and Discrete Element Model

Abstract

Advancement of EGS requires improved prediction of fracture development and growth during reservoir stimulation and long-term operation. This, in turn, requires better understanding of the dynamics of the strongly coupled thermo-hydro-mechanical (THM) processes within fractured rocks. We have developed a physics-based rock deformation and fracture propagation model by using a quasi-static discrete element model (DEM) to model mechanical rock deformation and fracture propagation induced by thermal stress. Various processes, such as heat exchange between fluid-filled fractures and solid rock, heat conduction through low-permeability matrices and associated mechanical deformations are all incorporated into the coupled model. The model predictions clearly indicate that under small to moderately large thermal strain load, thermal cracks grow into an array of parallel cracks and form a quasi-hierarchy of crack spacing and length. We further demonstrate that under large thermal strain load, the final crack pattern changes from an array of approximately hierarchically ordered parallel cracks into a more complicated morphology that involves fracture curving and arrest at multiple stages.