Study on Fault Slip Mechanism During CO2 Flooding and Storage

During the process of CO2 flooding and storage, when the force applied to the faults exceeds their critical strength, they will slip and alter the original geological structure, which is one of the main causes leading to CO2 leakage. This study simulated the fault slip behavior under various CO2 injection rates, horizontal distances between the injection point and the fault, and different fault scales through a multi-field coupling numerical model. It defined the fault slip coefficient and revealed the fault slip trend and potential leakage pathways of CO2 by analyzing the coupling effect of injection pressure, pore fluid, and fault mechanical response, providing an important theoretical basis for evaluating the safety of CO2 storage. The study indicates that the fault slip behavior presents significant spatiotemporal evolution characteristics, and the slip process shows an obvious nonlinear growth trend. Under the condition of large-scale faults, with the increase of the distance between the injection point and the fault and the decrease of the CO2 injection rate, the fault slip amount significantly reduces, and the slip initiation time gradually extends. In the near-field region, the effect of rapid pressure accumulation predominates, and the influence of the CO2 injection rate is relatively weakened. In the far-field region, the impact of the CO2 injection rate on the initiation time of fault slip is more pronounced. During the process of CO2 injection, in contrast to large-scale faults, medium-scale faults and small-scale faults have steeper slope curves in the rapid growth stage of the slip curve, demonstrating weaker anti-slip ability and more pronounced mechanical response characteristics, and are more susceptible to injection disturbances. This study reveals the main controlling factors affecting the safety of fault slip during the process of CO2 flooding and storage, and their interaction mechanism, providing theoretical guidance for optimizing CO2 injection parameters, delaying fault slip and ensuring the safe storage of CO2.