Multiscale fracture networks and their impact on hydroshearing response in the Canadian Shield (Kuujjuaq, Canada)

Abstract

Understanding the natural fracture network is essential for geothermal-related investigations. However, the geometrical attributes depend on the scale of observation. Therefore, a multiscale characterization of the fracture network is essential to ensure that heat and flow simulations are based on stochastically generated discrete fracture network models representative of the natural fracture system observed. The objective of this project was to understand the scale effect of fracture data on the performance of a potential enhanced geothermal system in crystalline rock in northern Canada. This was accomplished by collecting and characterizing fracture data from core, outcrops and satellite image, and then constructing a discrete fracture network model which was used to simulate the performance of the geothermal system. The numerical simulations suggest that fracture length and spacing have an important impact on its performance. Thermal short-circuiting can be easily achieved if the fracture network is modelled based solely on satellite image data, and hydroshearing may be less effective if the DFN is constructed based solely on outcrop data. The simulations suggest that combining the different datasets provides the best compromise between heat extraction, water losses, hydraulic impedance and thermal drawdown. Despite the uncertainties, the fracture data used highlights the importance of multiscale fracture analysis for heat-flow simulations of geothermal reservoirs.