Fault stability and sealing capacity evolution during CO2 geological sequestration on different injection strategies

There are inevitable faults in the strata of CO2 geological storage, and CO2 injection can easily alter fault's stability and closure capacity. Usually, stability and closure issues occur together and interactively affect. A hydro-mechanical coupling model for CO2 injection-production in fault-bearing strata is established, after considering the internal structure of fault and its contact behavior with strata. Subsequently, the evolution of stability and closure capacity under different injection locations, patterns fault types, and dip angles are studied comprehensively. The effects of discrete parameters (different fault forms and injection-production strategies) on fault stability and sealing capacity are studied. Through Sobol sensitivity analysis, we quantitatively explained the difficult-to-explore interactions of discrete variables. The results show that fault dip has less influence on stability and sealing capacity than other factors. Injection type has the most pronounced effect on stability, and fault type has the most pronounced effect on closure performance. A smaller dip angle ensures better safety among low-angle faults. For injection strategy, hanging wall injection and one-side or two-side injection also ensure both better stability and sealing capacity. The interaction effect of the factors in this research is significant. Reverse faults with 60°–70° dip and the sealing of normal faults are most sensitive to injection-production strategies, especially changes in injection type. Furthermore, in practical engineering, stability should be mainly monitored during injection, while sealing risk should be mainly monitored after injection process. This study provides valuable insights into fault safety analysis and CO2 leakage assessment, offering guidance for practical CO2 injection.