Exploration of Geothermal and Lithium Recovery Potentials: A Simulation Study of a Small-Scale CO2-Saturated Brine Injection in the Leduc Aquifer in Alberta, Canada

Abstract Geologic sequestration of CO2 generally involves injecting supercritical CO2 into deep saline aquifers. However, large-scale CO2 sequestration projects require significant capital investment. The objective of this study is to simulate a small-scale CO2-saturated brine injection pilot in the Simonette area of the Leduc Formation to investigate the feasibility of coupling geothermal energy production and lithium recovery to leverage the injection costs. A geothermal doublet system was simulated to produce in-situ hot brine, containing 79 mg/L lithium, from the Leduc aquifer. The produced brine was cooled down after being processed at a geothermal and lithium recovery plant. The cool brine was then mixed with CO2 at surface and reinjected back into the aquifer through another well (with a downhole distance of 3 km from the producer). The operating conditions of the doublet were based on pilot data from two major lithium recovery plants in Alberta, Canada. The doublet was simulated for 40 years of injection and 200 years of shut-in using thermo-hydro-mechanical simulation to assess the feasibility of injecting and containing CO2 in the aquifer. Simulation parameters (e.g., geomechanical and petrophysical data) were based on laboratory measurements and analysis of available field and well-test data. Simulation results indicate that the doublet (with a volumetric flow rate of 1,500 Sm3/day) could recover around 650 kg/day of lithium hydroxide monohydrate (LHM) using a direct lithium extraction (DLE) method. The results also suggest that the production well could produce approximately 3.2 to 9.7 tonnes of CO2 daily. This is much lower than the amount of CO2 needed to saturate the brine after being cooled in a heat exchanger of a geothermal power plant. Nonetheless, the reinjected brine was fully saturated with CO2 to account for other sources of CO2 from nearby factories, such as Keyera’s Simonette Gas Plant. The reinjected brine could stay dissolved underground due to high reservoir pressure, despite the in-situ fluid being hotter than the reinjected brine. Furthermore, well spacing was wide enough to avoid CO2 production within the simulated timeframe. More importantly, analysis of the results indicate that the geothermal doublet could generate around 0.34 MWe, partially supporting the subsequent lithium recovery operations. The thermo-hydro-mechanical simulation output suggests the possibility of a strong undrained thermoporoelastic response in low-permeability underburden areas due to the injection of cool CO2-saturated brine, inducing significant thermal stress. Furthermore, there is a high chance of fault reactivation near the injection well within the aquifer. Although rock failure within the aquifer would not necessarily jeopardize the containment of CO2, it could potentially affect wellbore stability, particularly when there is a possibility of fluid-rock-casing interactions near the wellbore. This study provides, for the first time, practical insights into the feasibility of implementing a small-scale CO2-saturated brine injection pilot in the Leduc aquifer, while leveraging both geothermal energy and lithium recovery potential.