Numerical Simulation of Cement Sheath Integrity Under Stress-Corrosion Coupling in Carbon Injection Wells

The cement sheath of CO2 injection well (CCUS well) is extremely prone to failure of sealing integrity under the combined effects of complex loads and the acidic environment formed by the reaction of injected CO2 with formation water. Based on the theories of multiphase flow in porous media and continuum damage mechanics, the mechanical behavior of the cement sheath before and after corrosion was described by introducing corrosion-induced damage variables. A finite element model of the wellbore assembly considering the coupling effect of stress and corrosion was established using COMSOL software. The influence of casing internal pressure and corrosion time on the integrity of the cement sheath was analyzed and discussed. The results show that under higher casing internal pressure, the cement sheath undergoes elastoplastic deformation, and the interface between the casing and the cement sheath is easy to form a micro-gap. Due to the coupling effect of corrosion and casing internal pressure, the cement sheath is more susceptible to integrity failure. Compared with the uncorroded cement sheath, the equivalent plastic strain and micro-gaps of the corroded cement sheath after compression are both significantly larger, and the micro-gap is markedly affected by the corrosion time.