Numerical Assessment of the Geothermal and Thermal Energy Storage Potential of the Underground Con Mine (Northwest Territories, Canada)

Flooded mines constitute groundwater reservoirs that can be exploited with geothermal heat pump systems. Modelling such a reservoir is challenging because groundwater flow and heat transport equations need to be solved within the complex geometry of mine workings. To address this challenge, we developed a tridimensional numerical model to estimate the geothermal heat pump and underground energy storage potential, using the Con Mine near Yellowknife, Northwest Territories, Canada as an example. We used the finite element method to simulate the transient 3D temperature field within the water and in the rock mass. The shafts and tunnels of the mine are represented with 1D elements embedded in a tridimensional matrix. Hydraulic and thermal properties were evaluated at the mine site and in the laboratory with samples from outcrops and cores. The numerical model was calibrated to reproduce hydraulic head and temperature measured while pumping one of the shafts. Then, the long-term temperature of the water under different cases of geothermal heat pump operation was simulated for 25 years. The total energy delivered to buildings per year for a flow rate of 0.06 m3 s−1 was 953 MWh vs. 18,048 MWh when the pump depth was 0.3 vs 1 km. We also simulated heat production using solar thermal collectors to provide additional energy storage. The results suggest that it would be easier to increase energy production by augmenting the flow rate or by placing the pump at a greater depth than by adding solar collectors.