Monitoring-Based Study of Migration Characteristics of Highly Saline Mine Water During Deep Well Injection and Storage in the Ordos Basin

Deep well injection and storage (DWIS) has recently been proposed and implemented to achieve zero mine water emissions. In 2023, DWIS for highly saline mine water was successfully applied to a local mine in the Ordos Basin for the first time with excellent performance. However, the storage characteristics of highly saline mine water in the storage layer during DWIS remain unclear. This study was conducted in situ with real-time, online monitoring of instantaneous flow and injection pressure, along with synchronous micro-seismic monitoring during the early stages of DWIS, based on the geological conditions and spatial structure of the storage layer. The results indicated that the early seepage characteristics of the fluid geological storage did not conform to Darcy’s law. Within a certain pressure range, as the water pressure increased, the flow also increased. However, beyond this range, further increases in pressure caused a gradual decline in the flow. During the initial phase of storage, the migration of high-salinity mine water within the storage layer occurred in two stages: breakthrough and stabilization. During the breakthrough stage, the water injection pressure propagated to the flooding front, overcoming the formation stress and expanding the storage space. At this stage, mine water primarily filled the pore microcracks within the flooding front. In the initial 10 days of storage, high-salinity mine water in the study area affected approximately 42,104 m2 of the storage layer plane. The injection well affected an area nearly 200 m in depth, extending approximately 190 m northward and approximately 40 m upward. The predominant diffusion directions were northeast and east–southeast from the injection well. These findings could provide valuable insights into the treatment of highly saline mine water in the Ordos Basin, demonstrate the feasibility and safety of DWIS, and offer significant scientific contributions to the prevention and control of mine water pollution.