Transient H2O–CO2 wellbore leakage under evolving recharge conditions considering CO2 phase change

Abstract

Abandoned wells are one of the dominant pathways of deep CO2 leakage, threatening the safety and effectiveness of CO2 geological storage. Although CO2 wellbore flow has been discussed in several studies, the analysis of the CO2 wellbore leakage under evolving recharge conditions based on the transient wellbore-reservoir fully coupled model, which can describe the CO2 gas-liquid phase change, has yet to be reported. Thus, a transient wellbore-reservoir fully coupled model is established in this study to investigate the interaction between CO2 injection and wellbore leakage. The results show that the fluid wellbore leakage may cause significant disturbance to the reservoir and injection well, and the fluid leakage process can be divided into different stages according to the leakage and recharge characteristics. Besides, the wellhead temperature of the abandoned well shows a different variation trend compared with previous studies, which is attributed to the evolving reservoir recharge. The parameter analysis indicates that the gap aperture in the plugs of the abandoned well, plug locations, CO2 injection rate, and reservoir permeability have apparent effects on the fluid leakage rates but have little impact on the leakage pattern. Finally, a dimensionless parameter, the ratio of leakage to injection mass, is proposed to generalize the leakage degree, and the empirical relationship of the ratio of leakage to injection mass with time is established to facilitate quick estimation. This study broadens the understanding of CO2 wellbore leakage and provides a simple method to predict similar leakage scenarios approximately.