Modeling of possible CO2 leakage with phase transition in wellbore-reservoir system based on the Ordos CCS project, China

The leakage of injected CO2 through wellbores, during which the CO2 phase transition may occur, is a prime concern in CO2 deep saline aquifer storage projects. In this study, a two-dimensional non-isothermal wellbore-reservoir coupled model that can deal with the CO2 phase transition is established according to the Shenhua Ordos Carbon Capture and Storage (CCS) project in China. Different leakage scenarios through the injection well are simulated to explore the leakage characteristics and reveal the mechanism of important phenomena. The simulation results show that the CO2 leakage through the injection well in the Ordos CCS project, which takes thick multi-layered strata with unusual pressure distribution as the target reservoir, is self-limited, and the leakage stops after the reservoir pressure is offset with the pressure provided by the leaked groundwater in the wellbore. During the leakage, the liquid-phase or supercritical CO2 in the wellbore-reservoir system undergoes a certain degree of gasification, which has a strong and positive effect on the leakage. Moreover, although the leakage eventually stops at the wellhead, the crossflow between different injection layers through the wellbore continues. The parameter analysis indicates that the permeability and the initial and boundary pressure distribution of the reservoir play an important role in the CO2 leakage process, especially when they have a significant impact on the CO2 gasification in the reservoir. These results may provide a basis for evaluation, precaution, and management of similar wellbore leakage.

Automated summary

This study examines the leakage of injected CO2 through wellbores and explores the phenomena and characteristics associated with this leakage. The results show that the CO2 leakage in the Ordos CCS project is self-limited and eventually stops when the reservoir pressure is offset. Gasification of the CO2 during the leakage enhances the leakage process. Additionally, crossflow between different injection layers through the wellbore continues even after the leakage stops at the wellhead. The permeability and pressure distribution of the reservoir play crucial roles in the CO2 leakage process.