Multiscale Digital-Rock Investigation of Chemo-Mechanical and Flow Responses in Tight Sandstone under Sulfate-Rich Brine Sequestration

High-sulfate mine water from deep coal seams poses persistent safety and environmental challenges, while conventional treatment and disposal methods remain costly and unreliable. In contrast to the extensively studied CO2-rich acidic systems, the impacts of nonacidic, sulfate-rich brines on tight sandstone reservoirs remain poorly constrained. Understanding how sulfate-rich brine drives concurrent mineral transformation and hierarchical fracture evolution under deep geological confinement is critical for evaluating reservoir integrity during long-term mine water sequestration. To address this question, sandstones samples from the Liujiagou and Shiqianfeng formations were examined before and after mine water injection using multiscale digital rock imaging, lattice Boltzmann flow modeling, and finite discrete element simulations. Results indicate that micro–nanoscale dissolution enlarged pore throats and fractures, increasing porosity from 2.59 to 3.44%, connected pore volume by 166%, and permeability by 60%. Fractures were consistently observed across scales, indicating systematic fracture development. Although fracture formation reduced stiffness, mineral transformations and secondary cementation produced net gains of 14% in elastic modulus and 22% in compressive strength. These findings reveal a previously uncharacterized chemo-mechanical and flow evolution pathway driven by sulfate-rich, nonacidic brine and demonstrate that controlled deep mine water sequestration can both mitigate surface discharge risks and enhance long-term reservoir stability. This study provides a scientific foundation for integrating deep brine sequestration into sustainable environmental protection and subsurface resource management strategies.