Sealing Integrity Analysis of Cement Sheath Considering the Influence of Ground Stress and CO₂ Corrosion

In the process of CO₂ storage, the cement sheath of CCUS well may be exposed to the coupling of alternating stress and CO₂ corrosion, which greatly affects the sealing integrity of wellbore assembly. In this paper, the finite element analysis model of wellbore assembly considering the influence of the ground stress and the coupling effect of casing internal pressure and CO₂ corrosion is established by using ABAQUS software. The sealing integrity failure behavior of wellbore assembly under the coupling effect of casing internal pressure, corrosion time and ground stress is analyzed and discussed. The results show that under the coupling effect of high casing internal pressure and ground stress, the stress of cement sheath increases, and the unrecoverable large plastic strain occurs. The micro-gap is generated at the casing-cement sheath interface, and the wellbore integrity fails. Under the coupling effect of casing internal pressure, CO₂ corrosion and ground stress, corrosion has a positive response to the maintenance of the sealing integrity of the wellbore assembly at lower casing internal pressure. Due to the influence of ground stress, the micro-gap at the casing-cement ring interface is not significantly affected by the corrosion time. However, compared with the uncorroded cement ring, corrosion increases the critical pressure generated by the micro-gap, which has a certain positive effect on maintaining the sealing integrity of the wellbore assembly.