Development of a Numerical Tool for EGS-Layout Calculations Based on 3D XFEM Fracture Propagation Simulations and Laboratory Experiments on Large Rock Samples

Abstract

In view of engineering a heat exchanger at depth, we study the creation and optimization of fractures in basement rocks. To this end we developed a 3D fracture propagation code and verified it against laboratory hydraulic fracture experiments. Ultimately, the fracture propagation code will be coupled to an existing reservoir simulator for heat and mass transfer. It handles discontinuities, i.e. discrete fractures, by the particularly suited Extended Finite Element Method. A true-triaxial press allows verification of the code. Experiments comprise fluid-induced fracturing of rocks of a dimension of 300  300  450 mm³ under horizontal and vertical confining pressures up to 15 MPa and 30 MPa, respectively. Thirty-two ultrasonic sensors placed around the rock sample allow monitoring fracture propagation by recording and localizing the associated acoustic events during fracture propagation. The experiments help testing and improving the fracture propagation code. The ultimate goal is the development of a numerical design and layout tool for engineered geothermal systems.