Summary With this study, we present experimental and simulation investigations into microannulus generation at the casing/cement interface, a primary cause of integrity loss in the casing/cement/formation system. For the experiments, we used a full-scale apparatus, utilizing fiber Bragg grating (FBG) sensors to measure cement sheath deformation and monitoring leakage at the interface. The results demonstrate that under cyclic loading, plastic strain in the cement sheath accumulates and leakage of interface initiates during the unloading phase of a specific cycle (beyond the first one). Leakage correlates strongly with this accumulated plastic strain. We developed a finite element method (FEM) analysis, incorporating a nonlinear kinematic hardening plastic model to capture the cement sheath’s cyclic plasticity and the interface damage, to simulate the mechanical response and damage during cyclic loading. The analysis reveals that the formation and propagation of microannulus results from the combined effects of cyclic plasticity of cement sheath and interface damage. Plastic deformation in the cement sheath induces tensile radial stress during unloading, and this tensile stress intensifies with loading cycles, progressively leading to the damage of the interface. Additionally, we assess the threshold width of the microannulus for the onset of leakage and discuss its influencing factors.
Chen et al. (Sun,) studied this question.