Impact of fracture properties on the performance of engineered geothermal systems in the crystalline basement of Kuujjuaq (Canadian Shield)

Abstract

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 forward heat and flow simulations are based on stochastically generated discrete fracture network models representative of the natural fracture system observed. This was the goal of this work. Fracture data was collected from satellite imagery, outcrops and well cores to evaluate the scale effect and to study the impact of fracture size and density on the performance of engineered geothermal systems by numerical modeling. The numerical simulations highlighted that networks made of small fractures (0.08 to 27 m) tend to decrease the performance of the system compared to a network made of large fractures (22 to 1,437 m). However, thermal short-circuiting is easily reached in the latter scenario. Thus, the simulations suggest that the best-case network is made of fractures ranging between 1.57 to 135 m with fractures spaced by 5 m. This scenario 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.