Fault activity responses to CO2 injection revealed by similarity modeling

Fault activity at carbon storage sites is a critical factor governing the long-term safety of geological CO 2 sequestration. However, the mechanisms through which CO 2 injection influences fault behavior remain insufficiently understood. To address this issue, a large-scale three-dimensional physical similarity experiment was independently developed to simulate CO 2 injection into a fault zone, with real-time monitoring of strain and temperature variations in the surrounding rock throughout the injection process. The results demonstrate a robust correlation between strain and temperature responses, with the footwall formations exhibiting more significant variations than the hanging wall under the influence of CO 2 . Subsequent to injection, CO 2 initially migrates along the fault plane into the siltstone formation near the outlet. Thereafter, it diffuses preferentially into formations exhibiting higher water content, a phenomenon attributable to CO 2 –water–rock interactions. The continuation of injection results in the propagation of further diffusion along the fault into adjacent formations, confirming that the fault zone acts as a high-permeability conduit. Moreover, the pore-pressure increase induced by CO 2 injection is identified as the primary driver of fault activity alteration, based on rock failure theory and fracture propagation mechanics. These findings enhance the understanding of CO 2 -induced fault responses and provide valuable guidance for the safe implementation of geological carbon storage.