Zhang S J, Pu H, Xue K S, et al.Characteristics of thermal recharge of heterogeneous surrounding rock under geothermal exploitation in closed mines[J].Journal of Henan Polytechnic University(Natural Science) ,2026,45(6):39-50.

doi:10.16186/j.cnki.1673-9787.2026010045

Received:2026/01/29

Revised:2026/04/24

Published:2026/10/09

Characteristics of thermal recharge of heterogeneous surrounding rock under geothermal exploitation in closed mines

Zhang Shaojie1, Pu Hai1,2, Xue Kangsheng2, Qu Gaobo2

1.School of Mechanics & Civil Engineering， China University of Mining and Technology， Xuzhou  221116， Jiangsu，  China；2.State Key Laboratory of Intelligent Construction and Healthy Operation and Maintenance of Deep Underground Engineering， China University of Mining and Technology， Xuzhou  221116， Jiangsu， China

Abstract: Objectives To reveal the influences of fracture spatial distribution and operational parameters on the thermal recharge performance of surrounding rock during geothermal exploitation in closed mines， this paper investigates the thermal recharge characteristics of heterogeneous surrounding rock.  Methods Based on the two-dimensional discrete fracture network theory， a coupled thermo-hydro-mechanical （THM） model for seepage-heat-mechanical processes was established. The thermal recharge processes under uniform and three non-uniform fracture distributions were simulated. The Plackett-Burman experimental design was adopted to analyze the effects of 11 operational and reservoir parameters on thermal breakthrough time， 10-year cumulative mass flow， and cumulative thermal power output. Results Fracture spatial distribution affects surrounding-rock thermal recharge by altering pressure transmission and cold-fluid migration paths. Denser fractures near the injection well improve short-term flow rate and energy output but accelerate thermal breakthrough. Fracture enrichment between wells or near the production well delays cold front propagation yet brings limited improvement to overall transport capacity. Initial matrix permeability and rock specific heat capacity  exert significant influences on thermal breakthrough time. Initial reservoir pressure， matrix permeability， and rock specific heat capacity are the dominant factors controlling cumulative mass flow. No single dominant factor is identified for cumulative thermal power output， No single dominant factor is identified for cumulative thermal power output， for which matrix permeability contributes the most.  Conclusions The thermal recharge performance of surrounding rock is jointly governed by fracture spatial structure， reservoir physical properties， and operational parameters. Engineering design should balance energy output against long-term thermal breakthrough risk.

Key words: closed mine; geothermal exploitation; thermal recharge of heterogeneous surrounding rock; thermo-hydro-mechanical （THM） coupling; fracture distribution