Coupled Geomechanical and Geochemical Responses of Carbonate-Bearing Sandstone Reservoirs to CO₂ Injection: A Critical Review of Instability Mechanisms, Risk-Assessment Frameworks, and Implications for Energy Storage

Abstract

The safe and permanent geological storage of carbon dioxide (CO₂) in deep carbonate-bearing sandstone formations requires a rigorous understanding of the coupled geomechanical and geochemical responses of the host reservoir to sustained fluid injection. Fluid injection simultaneously raises pore pressure, reduces effective stress on pre-existing faults, triggers carbonate mineral dissolution under acidic CO₂-saturated brine, and drives heterogeneous permeability evolution, a set of interdependent processes whose combined effect on reservoir integrity, cap-rock seal security, and induced seismicity risk is not adequately captured by existing single-process risk assessment frameworks. This comprehensive review synthesizes 96 peer-reviewed studies published between 1980 and 2024 to characterize the mechanistic basis and field-scale consequences of these coupled responses in carbonate-bearing sandstones. We examine: (i) the theoretical framework linking pore pressure increase, Biot effective stress reduction, and Coulomb failure on critically stressed faults; (ii) the geochemistry of carbonate dissolution under CO₂-acidified brine, including reaction kinetics, dissolution regimes, and their dependence on mineralogical composition; (iii) the coupled evolution of permeability anisotropy under combined mechanical and chemical loading; (iv) the mechanisms of cap-rock integrity failure including hydraulic fracturing, fault reactivation, capillary leakage, and wellbore cement degradation; (v) quantitative evidence from active geological carbon storage (GCS) sites including Sleipner, In Salah, Decatur, and Otway; and (vi) the limitations of current continuum-scale risk assessment practice. We identify four critical gaps in the literature and propose a six-phase integrated geomechanical-geochemical risk assessment framework for GCS operations in carbonate-bearing formations. The framework directly addresses the systematic underestimation of geomechanical instability risk arising from the failure to couple dissolution-driven permeability evolution with mechanical stability analysis in current engineering practice.