Coupled Thermo-Hydro-Chemo-Mechanical Processes in Rock Fracture: Implications for Long-Term Subsurface Carbon Sequestration Integrity

The injection of CO₂ into deep geological formations triggers a complex network of coupled geochemical and geomechanical processes. While reservoir pressure assessments often treat rock strength as a static parameter, the introduction of CO₂ alters the subsurface environment by acidifying the resident pore fluids. This acidic brine promotes the dissolution of carbonate and silicate mineral cements that maintain structural integrity. Simultaneously, high fluid injection pressures reduce the effective confining stress of the formation. This interaction drives time-dependent subcritical crack propagation, allowing micro-fractures to grow slowly over decades or centuries at stresses below the instantaneous failure threshold. If these fractures extend into the low-permeability caprock seal, containment security is compromised. This review synthesizes current advancements in laboratory triaxial testing, micro-computed tomography, and reactive transport modeling (RTM) to map these multi-physics interactions. By evaluating data from key field cases—including Sleipner, In Salah, and Weyburn-Midale, we demonstrate that isolated hydraulic or chemical assessments are insufficient. Ensuring permanent carbon storage requires an integrated thermo-hydro-chemo-mechanical (THMC) framework that treats the subsurface as a dynamic, fully coupled system.