Numerical Study of the Thermo-Hydro-Mechanical Coupling Impacts of Shallow Geothermal Borehole Groups in Fractured Rock Mass on Geological Environment

Yujin Ran, Jia Peng, Xiaolin Tian, Dengyun Luo, Bin Yang, Peng Pei () and Long Tang
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Yujin Ran: Guizhou Shallow Geothermal Energy Development Co., Ltd., Zunyi 563006, China
Jia Peng: Guizhou Shallow Geothermal Energy Development Co., Ltd., Zunyi 563006, China
Xiaolin Tian: Guizhou Shallow Geothermal Energy Development Co., Ltd., Zunyi 563006, China
Dengyun Luo: Guizhou Shallow Geothermal Energy Development Co., Ltd., Zunyi 563006, China
Bin Yang: College of Mines, Guizhou University, North Wing Rm. 426, Guiyang 550025, China
Peng Pei: College of Mines, Guizhou University, North Wing Rm. 426, Guiyang 550025, China
Long Tang: School of Mines, China University of Mining and Technology, Xuzhou 221116, China

Energies, 2024, vol. 17, issue 6, 1-22

Abstract: Fractured rock mass is extensively distributed in Karst topography regions, and its geological environment is different from that of the quaternary strata. In this study, the influences on geological environment induced by the construction and operation of a large-scale borehole group of ground source heat pumps are analyzed by a thermo-hydro-mechanical (THM) coupling numerical model. It was found that groundwater is redirected as the boreholes can function as channels to the surface, and the flow velocity in the upstream of borehole group is higher than those downstream. This change in groundwater flow enhances heat transfer in the upstream boreholes but may disturb the original groundwater system and impact the local geological environment. Heat accumulation is more likely to occur downstream. The geo-stress concentration appears in the borehole area, mainly due to exaction and increasing with the depth. On the fracture plane, tensile stress and maximum shear stress simultaneously occur on the upstream of boreholes, inducing the possibility of fracturing or the expansion of existing fractures. There is a slight uplift displacement on the surface after the construction of boreholes. The correlations of the above THM phenomena are discussed and analyzed. From the modeling results, it is suggested that the consolidation of backfills can minimize the environmental disturbances in terms of groundwater redirection, thermal accumulation, occurrence of tensile stress, and possible fracturing. This study provides support for the assessment of impacts on geological environments resulting from shallow geothermal development and layout optimization of ground heat exchangers in engineering practices.

Keywords: borehole group; karst fracture; thermo-hydro-mechanical coupling; numerical simulation; geological environment (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2024
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