3D Analysis of Thermo-poroelastic Processes on Fracture Network Deformation and Induced Micro-Seismicity Potential in EGS

摘要

This study presents three dimensional (3D) analyses of a fracture network in an Enhanced Geothermal System (EGS) with special emphasis on the role of hydraulic fracture/natural mechanical interactions and coupled thermo-poromechanical processes. The behavior of the system is modeled by coupling a thermo-poroelastic displacement discontinuity (DD) method (for fracture opening and shear, fluid and heat diffusion in the reservoir matrix) with a finite element method (for fluid flow and heat transport inside the fractures). The nonlinear characteristics of fracture opening and shear deformation are taken into account. The resulting method is then used to simulate an injection/production processes into/from a synthetic fracture network consisting of a major fracture intersected by a set of smaller natural fractures. Injection/production into/from the fracture network results in gradual shearing of the fractures that impacts the thermo-hydro-mechanical characteristics of the fracture system. It is also shown that the early micro-seismic events can be associated with fracture slip on smaller connected fractures due to thermal perturbation. Continued injection leads to stress intensity conditions favorable for fracture propagation in shear and tensile modes, which could increase the reservoir surface area and further contribute to seismicity.