Mine-oriented low-enthalpy geothermal exploitation: A review from spatio-temporal perspective

Highlights: • Mine-oriented geothermal system within the Earth Critical Zone was proposed. • 44 examples of mine-oriented geothermal projects were presented and classified. • Spatio-temporal feasibility study on mine-oriented geothermal system is requisite. • Reservoir recharge and structural feature play crucial role in its sustainability. Based on 44 documented demonstration projects worldwide, a novel conceptual aspect of mine-oriented low-enthalpy geothermal exploitation classification was initially proposed. For this new classification, special attention was paid to a spatio-temporal perspective. From the first temporal perspective, i.e. life-cycle of a mine, the projects implemented in mine legacy phase are dominated (55%), followed by production stage (36%). From the second space point of view, the low-enthalpy geothermal heat, i.e. ~<2000 m depth within the Earth's Critical Zone (corresponding to the earth temperature < 85 °C), can be recoverd using different geothermal media such as solid-mine rock stratum (7%), liquid-mine water (79%) and gas-mine ventilation exhaust (14%) in open pits and/or underground mines. Next, several engineering issues were discussed, including configurations, parameters, hydro-thermo-geological conditions etc., to analyze their effects on the performance and sustainability of dominated mine water-based geothermal systems. Another key outcome of this review is to apply three methods: theoretical analysis, numerical simulation and experimental test, on mine water-based scenario to acquire the current status of the feasibility study. Moreover, an analytical conceptual model, mainly focusing on the structural characteristics of long-wall coal mining gobs, shafts and galleries, was developed to preliminarily evaluate the static and dynamic geothermal potential of flooded Jiahe colliery with the traditional volume method. It is hoped that the findings, viewpoints and suggestions obtained from this review can be served as references for real geothermal installations associated with mine sites in the future.