Geothermal extraction performance of abandoned mines with roadway-goaf structures: coupled thermo-hydraulic simulation and techno-economic assessment

The utilization of geothermal energy from abandoned mines represents a crucial pathway for decarbonizing district heating and resource recycling, playing a significant role in achieving carbon neutrality. The complex underground structures and uncertainties in thermal and economic performance present substantial challenges for system design. To address this, this study integrates rigorous physical simulations with techno-economic optimization framework. Using China's Jiahe abandoned coal mine as a case study, a refined 3D coupled hydro-thermal model was developed, explicitly incorporating strata, roadways, and goafs. Simulations indicate that lowering reinjection temperatures and increasing mass flow rates enhance heat extraction but accelerate reservoir thermal drawdown. Furthermore, well layout fundamentally governs fluid residence time and heat recovery capacity. Moving beyond conventional single-variable analyses, the Taguchi method and Response Surface Methodology (RSM) were employed to quantify the sensitivity of the well layout plan, reinjection temperature, and mass flow rate. The results demonstrate that the well layout is the dominant factor affecting the Levelized Cost of Heat (LCOH) and payback period, whereas the Net Present Value (NPV) is jointly influenced by the well layout and reinjection temperature. Through multi-objective optimization using a desirability function, the optimal configuration was identified as well layout plan 2, with a reinjection temperature of 10 °C and a mass flow rate of 207.6 m 3 /h. This optimized scheme yields an LCOH of $30.16/MWh, an NPV of $3.47 million, and a payback period of 3.11 years. Ultimately, this integrated approach provides quantitative design guidelines for commercializing abandoned mine geothermal resources.