A multiphysics simulator for stope-coupled heat exchanger operation in deep underground mines

The ever-increasing mine depth offers unprecedented opportunities to access high-grade geothermal resources. By pre-installing pipeline systems in mined-out cavities before waste tailings placement, the stope-coupled heat exchanger (SCHE) has drawn growing attention for its superior socio-economic advantages. However, despite the extensive focus on energy efficiency, the system stability during heat production has been typically overlooked. This study therefore introduces a novel high-fidelity simulator for replicating practical SCHE operation. By embedding non-isothermal pipe flow into an evolutive thermo-poromechanics framework for cemented tailings, the outlet water temperature and multiphysics backfill response in diverse production settings are meticulously studied. Our calculations reveal for the first time that circulating chill fluid within mine backfill can substantially alleviate pressure development, suggesting enhanced system stability with heat-exchanger implementation. We also demonstrate that albeit targeting higher-grade geothermal resources, prioritizing cold-season operation, and pre-charging heat exchangers with production delays could spur heat productivity, the companion thermal pressure generation might still impose significant overloading risks. Conversely, while fast circulation would diminish the end-utilization temperature, the rapid heat removal could indeed facilitate superior efficiency and stability performance for the geothermal system. We believe these new findings hold critical implications for better positioning SCHE as a safely sustainable pathway towards hybrid utilization of deep resources.