Objective In some North China-type coalfield mining areas, a large volume of high-salinity mine water is generated during coal mining. These regions face dual challenges: high treatment costs to meet discharge standards, and the inefficient utilization and wasteful discharge of mine water resources. In recent years, the technology of deep reinjection and storage of high-salinity mine water has provided a new solution to this dilemma. Among the key issues, understanding the flow field evolution and the induced safety problems during mine water reinjection serves as an essential foundation and prerequisite for the reliable application of this technology.
Methods Taking Mine A as an example, the analytic hierarchyprocess (AHP) is used to optimize the selection of deep reinjection target aquifers. The evolution process of the groundwater hydrodynamic field under long-term reinjection conditions is simulated, and a technical system for safety assessment covering the entire life cycle of reinjection is established. A comprehensive safety impact assessment is conducted on potential water inrush hazards, so as to ensure the safe reinjection of mine water.
Results and Conclusions (1) By considering storage capacity, recharge–runoff–discharge and structural conditions, microscopic pore structures of the reservoir, and the quality characteristics of reinjection water, a suitability evaluation framework for target reinjection strata was established, through which the Ordovician Majiagou limestone aquifer was preferentially selected as the optimal reinjection formation. (2) A coupled underground–surface reinjection scheme was proposed, comprising underground “distributed, low-discharge, small-borehole” reinjection and surface “centralized, high-discharge, large-borehole” coordinated reinjection technologies. Based on this framework, three reinjection schemes were developed: four underground wells (total reinjection capacity of 400 m3/h), three surface wells (600 m3/h), and a combined configuration of two surface wells and two underground wells (600 m3/h). (3) Under a 30-year reinjection scenario, the simulated groundwater level increases for the three schemes were 22, 29, and 26 m, respectively. Cross-validation using empirical equations further demonstrated that the combined reinjection scheme with two surface wells and two underground wells was the most suitable. (4) Four potential water inrush scenarios induced by reinjection were systematically assessed for safety risks. For the coal seam floor, the water inrush coefficient increased by 2.2%–8.2% after reinjection, remaining below the critical safety threshold of 0.06 MPa/m, thereby exerting limited impact on safe coal extraction. In terms of faults and collapse columns, the F16 fault and Collapse Column 3, which were significantly influenced by reinjection, were analyzed, and an additional 7 m coal pillar was found sufficient to ensure mining safety. For bedrock outcrops, both lateral recharge pathways associated with concealed bedrock outcrops after reinjection exhibited relatively low water inrush risks. For borehole casing instability, under a 5 MPa Ordovician limestone hydraulic pressure in underground reinjection wells, COMSOL simulations and theoretical calculations both indicated that the maximum water inflow under four instability scenarios increased with borehole diameter. Considering the mine drainage capacity of the study area, the risk associated with instability-induced water inrush from a 75 mm borehole remained manageable. These findings provide a theoretical basis for optimizing and evaluating the safety of long-term high-salinity mine water reinjection schemes and have already been implemented in the Juye mining area of the North China coalfield, offering significant theoretical and practical implications for regional mine water conservation and reinjection risk control.
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