Risk assessment framework for closed wellbore sealing integrity failure under corrosion environment in CO2 geological sequestration

Abstract

Ensuring the long-term sealing integrity of closed wellbores is of crucial significance during the process of CO₂ geological sequestration. However, under the intense corrosive environment, the combined structure of cement plugs and casings may be damaged. This study presents a comprehensive risk assessment framework for sealing integrity failure through a variety of methodology: Initially, a numerical simulation-derived dataset was generated to characterize system behavior under multi-physics coupling conditions. Subsequently, a hybrid machine learning architecture integrating K-means clustering and Radial Basis Function Network (K-RBFN) was developed for remaining life prediction. The failure probability was then quantified via Monte Carlo simulations. Ultimately, risk assessment was achieved through consequence-of-failure weighted probability integration. The analysis results demonstrate that the average failure probability shows a continuous upward trend, and growth rate gradually accelerates, with the probability of failure increasing by 1 per cent after one century. The risk of failure is generally divided into three phases over the course of a century: (1) a latent risk period of 0–30 years (2) a slow growth period of 30–70 years (3) a rapid growth period after 70 years. Finally, through the established risk assessment framework, the failure probability and failure risk under three geological condition scenarios and five reservoir depths scenarios were analyzed. The failure risk assessment framework for the sealing integrity of closed wellbores under the corrosive environment of CO₂ geological sequestration established in this paper can provide a basis for the safety of engineering practice and help prevent potential engineering disasters.