Comparing Simulations and Experiments for Hydraulic Fracture Stimulations Performed at the Grimsel Test Site, Switzerland

Abstract

To research Deep Geothermal Energy, reservoir permeability enhancement by hydraulic fracturing has been studied at the Deep Underground rock Laboratory (DUG Lab) at the Grimsel Test Site (GTS), Switzerland. The test site consists of granodiorite with a low fracture density. Various boreholes have been subjected to stimulation phases at various locations along each borehole. Stimulation was repeated a number of times for each borehole location. Pressure and flow rate changes in the wellbore and packer interval as well as microseismicity were recorded for all stimulation phases. Modeling of the stimulations was performed with LLNL's GEOS. The GEOS framework allows fully hydro-mechanically coupled 3D simulations of rock deformation, LEFM fracture mechanics, fluid flow in fracture and matrix, and the generation of micro-seismic events. Focus areas are the fracture length and orientation, changes in hydraulic reservoir properties and the modeling of pressure behaviour during injection, shutin and post shut-in. This enables us to tie recorded data during the experiment, such as micro seismcic events, closer to the simulation and further our physical understanding.