Hydrodynamic evolution simulations and safety assessment of the deep reinjection and storage of high-salinity mine water

Authors

• XU Zhimin, School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China;Yunlong Lake Laboratory of Deep Underground Science and Engineering, Xuzhou 221116, China;National Professional Center Laboratory for Basic Research on Mine Water Hazard Prevention and Control Technology, Xuzhou 221116, ChinaFollow
• CHEN Weixiao, School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China;Yunlong Lake Laboratory of Deep Underground Science and Engineering, Xuzhou 221116, ChinaFollow
• SUN Yajun, School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China;National Professional Center Laboratory for Basic Research on Mine Water Hazard Prevention and Control Technology, Xuzhou 221116, China
• ZHANG Jian, School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China
• CHEN Tianci, School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China
• LIU Qi, School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China
• CHEN Ge, School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China
• HUA Jingfan, School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China

Abstract

Objective In some mining areas of North China-type coalfields, large volumes of high-salinity mine water produced during coal mining pose dual challenges: high treatment costs to meet discharge standards and the waste of mine water resources due to inefficient utilization before discharge. In recent years, the deep reinjection and storage technology for high-salinity mine water has provided a new approach to this issue. To achieve this technology, it is essential to understand the flow field evolution during mine water reinjection and address reinjection-induced safety problems. Methods This study investigated coal mine A in Jiangsu Province as an example. Using the analytic hierarchy process (AHP), this study determined the optimal target aquifer for deep reinjection of mine water. Then, the evolutionary process of the groundwater dynamic field under long-term reinjection was simulated. Accordingly, a technical system for assessing the safety throughout mine water reinjection was established. This system enabled a comprehensive safety risk assessment of potential water inrush sources, aimed at ensuring safe mine water reinjection. Results and Conclusions An assessment system for the suitability of target aquifers was developed, involving the storage conditions, recharge-runoff-discharge and structure conditions, microscopic reservoir pore structures, and mine water quality characteristics of the study area. Through fine-scale analysis using this system, the limestone aquifer of the Ordovician Majiagou Formation was selected as the optimal target. An underground-surface combined reinjection technique was proposed, comprising (1) underground reinjection characterized by the distributed arrangement, low flow rates, and small diameters of boreholes and (2) surface collaborative reinjection featuring the centralized arrangement, high flow rates, and large diameters of boreholes. Using this technique, three reinjection schemes were designed: four underground boreholes (total reinjection capacity: 400 m³/h), three surface wells (total reinjection capacity: 600 m³/h), and a combination of two surface wells and two underground wells (total reinjection capacity: 600 m³/h). Simulations reveal that under 30-year reinjection, the three reinjection schemes increased the groundwater level by 22 m, 29 m, and 26 m. Cross-validation based on an empirical equation demonstrates that the combination of two surface wells and two underground wells was the optimal reinjection scheme. Safety risk assessment was conducted for four potential water inrush patterns driven by mine water reinjection: water inrushes arising from coal seam floors, faults and collapse columns, the lateral recharge of concealed bedrock outcrops, and borehole casing instability. In terms of water inrushes from coal seam floors, the post-reinjection water inrush coefficients of the Ordovician limestone aquifer increased by 2.2%–8.2%, remaining below the safety threshold of 0.06 MPa/m. This result suggests that mine water reinjection exerted a limited impact on safe coal mining. Regarding water inrushes induced by faults and collapse columns, analysis of the F16 fault and the No. 3 collapse column, which are significantly affected by reinjection, indicates that safe coal mining can be ensured by increasing the collapse column thickness by 7 m. From the perspective of bedrock outcrops, two lateral recharge pathways of concealed bedrock outcrops would induce low water inrush risks. In terms of water inrushes induced by borehole casing instability, four boreholes with distinct diameters were investigated through simulations using the COMSOL software and theoretical calculations. The results indicate that, under 5 MPa water pressure of the Ordovician limestone aquifer in underground reinjection boreholes, casing instability-induced maximum water inflow volumes from the four boreholes increased with the borehole diameter. In combination with the underground drainage capacity of the study area, the water inrush risk induced by borehole instability was controllable in the case of a borehole diameter of 75 mm. The results of this study can provide theoretical support for both the selection of the optimal scheme and safety assessment for long-term reinjection of high-salinity mine water. The results have found widespread application in the Juye mining area of a North China-type coalfield, demonstrating that they hold great theoretical and practical value for regional mine water conservation, as well as the prevention and control of reinjection-associated risks.

Keywords

high-salinity mine water, deep reinjection, target aquifer selection for mine water reinjection, flow field evolution, numerical simulation, safety assessment

DOI

10.12363/issn.1001-1986.26.03.0176

Recommended Citation

XU Zhimin, CHEN Weixiao, SUN Yajun, et al. (2026) "Hydrodynamic evolution simulations and safety assessment of the deep reinjection and storage of high-salinity mine water," Coal Geology & Exploration: Vol. 54: Iss. 6, Article 16.
DOI: 10.12363/issn.1001-1986.26.03.0176
Available at: https://cge.researchcommons.org/journal/vol54/iss6/16

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