Geomechanical responses of reservoirs to cold CO2 injection: implications for carbon capture and storage

To enable the upscaling of carbon capture and storage, robust geomechanical derisking is essential for minimising induced seismicity and preserving reservoir containment. Conventional screening approaches typically focus on maximum sustainable injection pressures, yet when cold supercritical CO2 is injected into hot reservoirs, thermal contraction induces additional stress perturbations that may significantly impact fault stability. This is particularly relevant for basins with elevated geothermal gradients, such as Australia’s Cooper Basin. In this study, we present a coupled poro-thermo-elastic analysis demonstrating that pore pressure and temperature perturbations affect principal stresses asymmetrically, producing complex Mohr circle evolution that varies across stress regimes. This asymmetry means the fault orientation most susceptible to reactivation depends on the stress state at failure rather than initial conditions, complicating conventional assessment approaches. To address this challenge, we introduce a pressure–temperature (P-T) stability diagram that directly links operational parameters to reactivation thresholds, enabling visualisation of safe operating envelopes and identification of governing stress pairs without iterative analysis. Our findings indicate that geomechanical analyses focused solely on pore pressure may mischaracterise reactivation risk, and coupled poro-thermo-elastic approaches are essential for accurate screening of CO2 storage sites.