Influence of formation dip angle and injection strategy on CO2 wellbore leakage with consideration of CO2 transient flow and phase transition

CO2 leakage along defective wellbores is a common concern that threatens the effectiveness and safety of CO2 geological storage. Formation dip angle and CO2 injection strategy are recognized as key parameters that control CO2 migration within the reservoir after CO2 injection. It is therefore reasonable to hypothesize that these factors also have a significant influence on CO2 leakage along wellbores. However, to date, there has been a lack of research specifically addressing this issue. In this study, we employ a fully coupled wellbore-reservoir model that characterizes the transient flow of CO2-H2O and CO2 phase transitions to systematically investigate, the impacts of formation dip angle, CO2 injection strategy, and their synergistic effects on CO2 leakage along a defective wellbore. The results indicate that the formation dip angle, which controls buoyancy effects, significantly impacts CO2 leakage rates, with opposite trends depending on the relative positions of the leakage and injection wellbores. The influence of the CO2 injection strategy on CO2 leakage along the wellbore is modulated by the formation dip angle and wellbore positions. It primarily affects CO2 leakage by altering the CO2 breakthrough time and the distribution range of the CO2 plume within the reservoir. Additionally, during the non-injection period of periodic injection, increased groundwater recharge raises the leakage wellbore pressure, which has a certain inhibitory effect on CO2 leakage. These findings provide valuable insights and can serve as fundamental references for site selection, injection design, and leakage risk assessment in CO2 geological storage projects.