Time-evolution of ScCO₂-weakened coal integrity: Chemo-hydromechanical coupling and geological sequestration implications

Abstract

Geological sequestration of CO₂ is critical for deep decarbonization, but the geomechanical stability of coal reservoirs remains a major challenge. This study integrates nanoindentation, XRD/SEM-EDS chemo physical characterization and 4D CT visualization to investigate the time-evolving mechanical degradation of bituminous coals with ScCO₂ injection. The main results show that 4 d of ScCO₂ treatment caused 50.47%-80.99% increase in load-displacement deformation and 26.92%-76.17% increase in creep depth at peak load, accompanied by 55.01%-63.38% loss in elastic modulus and 52.83%-74.81% reduction in hardness. The degradation exhibited biphasic kinetics, characterized by rapid surface-driven weakening (0-2 d), followed by stabilized matrix-scale pore homogenization (2-4 d). ScCO₂ preferentially dissolved carbonate minerals (dolomite), driving pore network expansion and interfacial debonding, while silicate minerals resisted dissolution but promoted structural homogenization. These coupled geochemical-mechanical processes reduced the mechanical heterogeneity of the coal and altered its failure modes. The results establish a predictive framework for reservoir stability assessment and provide actionable insights for optimizing CO₂ enhanced coalbed methane recovery.

Keywords

CO₂ sequestration / Nanoindentation / Reservoirs stability / Coal mechanics

Acknowledgments

This work was supported by the National Natural Science Foun-dation of China (Nos. 52204206 and U24A2090) and the Funda-mental Research Funds for the Central Universities of China (No. 2023CDJXY-006).

Supplementary material

Supplementary data to this article can be found online at https://doi.org/10.1016/j.ijmst.2025.05.006.

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