Coupled analysis of non-isothermal flow and well patterns for heat extraction performance in mine geothermal systems

Abstract

Deep mining has become an inevitable choice for mineral resource development. However, the high-temperature environment in depth poses significant challenges to mine safety and production. In order to utilize the deep high geotemperature, this paper employs a synergistic cooling technology based on geothermal advance mining. This technology converts thermal hazards into energy while providing an optimal temperature environment for deep mining, achieving a novel mode of advance mining for geothermal extraction coupled with rock mass cooling. A three-dimensional, multi-fracture thermo-hydro coupled heat and mass transfer numerical model was established for the Sanshan Island Gold Mine. Under thermo-hydraulic coupling conditions, the effects of different wellbore models, well spacing parameters, and well layout patterns on thermal extraction performance and cooling efficiency were evaluated. The results indicate that the accuracy of wellbore modeling is a critical factor influencing the reliability of geothermal system performance evaluation. The use of a simplified wellbore model (representing the geothermal well within a Darcy flow physics interface) leads to a significant overestimation of key performance metrics—specifically, a 42.7% overestimation in production temperature and an overestimation of cumulative heat extraction by 9.3×10¹⁴ J. This study redefines optimal well spacing and spacing schemes in the context of non-isothermal wellbore frameworks. Well spacing parameter analysis reveals that the main flow channel widens as spacing increases, causing production temperature to rise and production flow rate to decrease, while total heat production initially increases before decreasing. Results demonstrate that an optimal well spacing of 225–250 m enables cumulative heat production to exceed 1.75×10¹⁵ J over 30 years. The one-injection-two-production model exhibited superior performance in both thermal recovery efficacy and cooling, achieving a 73% increase in total heat production compared to the conventional one-injection-one-production model.

Keywords

geothermal extraction / deep mining / different wellbore model / well layout patterns / thermal extraction performance

References

[1] Ranjith P G, Zhao J, Ju M-h, et al.. Opportunities and challenges in deep mining: A brief review [J]. Engineering, 2017, 3(4): 546-551.

[2] An H-m, Mu X-hai. Contributions to rock fracture induced by high ground stress in deep mining: A review [J]. Rock Mechanics and Rock Engineering, 2025, 58(1): 463-511.

[3] Guo Q-f, Xi X, Yang S-t, et al.. Technology strategies to achieve carbon peak and carbon neutrality for China’s metal mines [J]. International Journal of Minerals, Metallurgy and Materials, 2022, 29(4): 626-634.

[4] Cai M-f, Li P, Tan W-h, et al.. Key engineering technologies to achieve green, intelligent, and sustainable development of deep metal mines in China [J]. Engineering, 2021, 7(11): 1513-1517.

[5] Li P, Cai M-f, Miao S-j, et al.. Mechanism, prevention, and control of mining-induced dynamic disasters in underground metal mines in China: Challenges and solutions [J]. Journal of Central South University, 2024, 31(8): 2549-2606.

[6] Li J-g, Zhan K. Intelligent mining technology for an underground metal mine based on unmanned equipment [J]. Engineering, 2018, 4(3): 381-391.

[7] Li P, Cai M-feng. Challenges and new insights for exploitation of deep underground metal mineral resources [J]. Transactions of Nonferrous Metals Society of China, 2021, 31(11): 3478-3505.

[8] Ran Y-j, Peng J, Tian X-l, et al.. Technologies for heat hazard governance and thermal energy recovery in deep mines [J]. Energies, 2024, 17(6): 1369.

[9] Strzemecka J, Goździewska M, Skrodziuk J, et al.. Factors of work environment hazardous for health in opinions of employees working underground in the ‘Bogdanka’ coal mine [J]. Annals of Agricultural and Environmental Medicine, 2019, 26(3): 409-414.

[10] Li N-p, Shu H-m, Sun D-yuan. Human thermal comfort indicator in high-temperature environments in deep mining [J]. Journal of Safety and Sustainability, 2025, 2(2): 134-141.

[11] You B, Chen Y-s, Yang M, et al.. Management of thermal hazards in deep mines in China: Applications and prospects of mine cooling technology [J]. Water, 2024, 16(16): 2347.

[12] Shi H-q, Sun H, Jiang Y-y, et al.. Ecological characteristics and OccupationalHealth effects of deep mines in China: A review [J]. Polish Journal of Environmental Studies, 2024, 33(3): 2515-2525.

[13] Ding L-w, Zhang Z-t, Li B-y, et al.. Feasibility investigation of geothermal energy heating system in mining area: Application of mine cooling and aquifer thermal energy exploitation technique [J]. Energies, 2024, 17(5): 1168.

[14] Zhao J-l, Li Z-j, Xu Y, et al.. An integrated mine geothermal extraction and cooling system based on the holistic space utilization concept of mine [J]. Energy, 2025, 335: 137990.

[15] Nkinyam C M, Ujah C O, Asadu C O, et al.. Exploring geothermal energy as a sustainable source of energy: A systemic review [J]. Unconventional Resources, 2025, 6: 100149.

[16] Shi J-h, Li J-y, Li Y-t, et al.. Numerical investigation of hydrogen vapor cloud explosion from a conceptual offshore hydrogen production platform [J]. Journal of Safety and Sustainability, 2024, 1(4): 189-201.

[17] North J, Knibb S T, Ali S M F. The hydratherm hybrid drilling systems for cheaper heavy oil recovery [J]. Journal of Canadian Petroleum Technology, 2001, 40(5): 67-74.

[18] He M-chao. Research and development on hems cooling system and heat-harm control in deep mine [J]. China Basic Science, 2008, 10(2): 11-16

[19] Cai M-f, Brown E T. Challenges in the mining and utilization of deep mineral resources [J]. Engineering, 2017, 3(4): 432-433.

[20] Wu X-h, Cai M-f, Wu X, et al.. Impact of well placement and flow rate on production efficiency and stress field in the fractured geothermal reservoirs [J]. Deep Underground Science and Engineering, 2024, 3(3): 358-368.

[21] Tang M, Li H, Tang C-nan. Study on preliminarily estimating performance of elementary deep underground engineering structures in future large-scale heat mining projects [J]. Geofluids, 2019, 2019: 3456307.

[22] Zhang Y-j, Li Z-w, Yu Z-w, et al.. Evaluation of developing an enhanced geothermal heating system in Northeast China: Field hydraulic stimulation and heat production forecast [J]. Energy and Buildings, 2015, 88: 1-14.

[23] Zhao Y-j, Liu L, Wen D, et al.. Experimental study of horizontal ground heat exchangers embedded in the backfilled mine stopes [J]. Geothermics, 2022, 100: 102344.

[24] Xu Y, Li Z-j, Chen Y, et al.. Synergetic mining of geothermal energy in deep mines: An innovative method for heat hazard control [J]. Applied Thermal Engineering, 2022, 210: 118398.

[25] Xu Y, Li Z-j, Tao M, et al.. An investigation into the effect of water injection parameters on synergetic mining of geothermal energy in mines [J]. Journal of Cleaner Production, 2023, 382: 135256.

[26] Liu G, Zhou B-j, Liao S-ming. Inverting methods for thermal reservoir evaluation of enhanced geothermal system [J]. Renewable and Sustainable Energy Reviews, 2018, 82: 471-476.

[27] Ngoma M C, Kolawole O, Olorode O. Geothermomechanical alterations due to heat energy extraction in enhanced geothermal systems: Overview and prospective directions [J]. Deep Underground Science and Engineering, 2024, 3(3): 256-268.

[28] Jia Y-z, Tsang C F, Hammar A, et al.. Hydraulic stimulation strategies in enhanced geothermal systems (EGS): A review [J]. Geomechanics and Geophysics for Geo-Energy and Geo-Resources, 2022, 8(6): 211.

[29] Kumari W G P, Ranjith P G. Sustainable development of enhanced geothermal systems based on geotechnical research - A review [J]. Earth-Science Reviews, 2019, 199: 102955.

[30] Zhang L, Chen S, Zhang C. Geothermal power generation in China: Status and prospects [J]. Energy Science & Engineering, 2019, 7(5): 1428-1450.

[31] Zhang W, Wang D, Wang Z-l, et al.. Study on permeability evolution and damage mechanism along the EGS fracture in heat mining stage under thermal stress/cracking [J]. Geothermal Energy, 2023, 11: 31.

[32] Liu G, Zhou C-w, Rao Z-h, et al.. Impacts of fracture network geometries on numerical simulation and performance prediction of enhanced geothermal systems [J]. Renewable Energy, 2021, 171: 492-504.

[33] Asai P, Podgorney R, Mclennan J, et al.. Analytical model for fluid flow distribution in an Enhanced Geothermal Systems (EGS) [J]. Renewable Energy, 2022, 193: 821-831.

[34] Yu P-l, Dempsey D, Archer R. A three-dimensional coupled thermo-hydro-mechanical numerical model with partially bridging multi-stage contact fractures in horizontal-well enhanced geothermal system [J]. International Journal of Rock Mechanics and Mining Sciences, 2021, 143: 104787.

[35] Kihm J H, Park J Y, Lee S, et al.. Thermo-hydrological numerical evaluation of carbon dioxide injection efficiency for its geologic storage using a coupled reservoir-well simulation scheme [J]. International Journal of Greenhouse Gas Control, 2019, 90: 102623.

[36] Liu J, Cheng W-l, Nian Y-le. The stratigraphic and operating parameters influence on economic analysis for enhanced geothermal double wells utilization system [J]. Energy, 2018, 159: 264-276.

[37] Chen G, Wang Z-y, Sun X-h, et al.. A shut-in pressure calculation method for high-temperature high-pressure wells in deepwater fractured formations based on thermo-hydro-mechanical coupling [J]. Petroleum Exploration and Development, 2025, 52(2): 506-518.

[38] Liu D-d, Xiang Y-yong. A semi-analytical method for three-dimensional heat transfer in multi-fracture enhanced geothermal systems [J]. Energies, 2019, 12(7): 1211.

[39] Xie J-x, Zhu Z-l, Zhang J. Effect of natural fracture on the heat mining of enhanced geothermal system based on the thermo-hydro-mechanical coupling model [J]. International Journal of Green Energy, 2024, 21(11): 2405-2414.

[40] Wang S-h, Huang Z-q, Wu Y-s, et al.. A semi-analytical correlation of thermal-hydraulic-mechanical behavior of fractures and its application to modeling reservoir scale cold water injection problems in enhanced geothermal reservoirs [J]. Geothermics, 2016, 64: 81-95.

[41] BONGOLE K, SUN Zhi-xue, YAO Jun, et al. Multifracture response to supercritical CO₂-EGS and water-EGS based on thermo-hydro-mechanical coupling method [J]. International Journal of Energy Research, 2019: er. 4743. DOI: https://doi.org/10.1002/er.4743.

[42] Shi Y, Song X-z, Wang G-s, et al.. Numerical study on heat extraction performance of a multilateral-well enhanced geothermal system considering complex hydraulic and natural fractures [J]. Renewable Energy, 2019, 141: 950-963.

[43] Chen Z-y, Huang L-q, Li X-b, et al.. Comprehensive heat extraction performance and fractured reservoir cooling effect analysis of a novel mine enhanced geothermal system [J]. Applied Thermal Engineering, 2024, 245: 122790.

[44] Gao X-f, Zhang Y-j, Huang Y-b, et al.. Study on heat extraction considering the number and orientation of multilateral wells in a complex fractured geothermal reservoir [J]. Renewable Energy, 2021, 177: 833-852.

[45] Ma W-w, Chen Y-r, Wang Y, et al.. Multiparameter design and optimization of enhanced geothermal system based on unit effective permeable area [J]. Applied Thermal Engineering, 2023, 225: 120184.

[46] Asai P, Panja P, Mclennan J, et al.. Performance evaluation of enhanced geothermal system (EGS): Surrogate models, sensitivity study and ranking key parameters [J]. Renewable Energy, 2018, 122: 184-195.

[47] Wang G-l, Liu G-h, Zhao Z-h, et al.. A robust numerical method for modeling multiple wells in city-scale geothermal field based on simplified one-dimensional well model [J]. Renewable Energy, 2019, 139: 873-894.

[48] Ma F, Liu G-h, Zhao Z-h, et al.. Coupled thermo-hydro-mechanical modeling on the Rongcheng geothermal field, China [J]. Rock Mechanics and Rock Engineering, 2022, 55(8): 5209-5233.

[49] Aliyu M D, Chen H-peng. Sensitivity analysis of deep geothermal reservoir: Effect of reservoir parameters on production temperature [J]. Energy, 2017, 129: 101-113.

[50] Zhang J-c, Chen L, Sun Y-h, et al.. Geothermal resource distribution and prospects for development and utilization in China [J]. Natural Gas Industry B, 2024, 11(1): 6-18.

[51] Ma Y-y, Li S-b, Zhang L-g, et al.. Study on the effect of well layout schemes and fracture parameters on the heat extraction performance of enhanced geothermal system in fractured reservoir [J]. Energy, 2020, 202: 117811.

[52] Madani M, Sharifi M. Effects of permeability heterogeneity on heat extraction performance in geothermal reservoirs with carbon dioxide working fluid [J]. Energy, 2025, 324: 136007.

[53] Madani M, Sharifi M. Multi-faceted numerical investigation into heat extraction performance of horizontal doublet fractured geothermal reservoirs with carbon dioxide working fluid [J]. Renewable Energy, 2025, 249: 123180.

RIGHTS & PERMISSIONS

Central South University