LAUSR

Abstract The sustained casing pressure (SCP) occurring during multistage fracturing in shale gas wells is an important problem to solve. This paper presents experimental and numerical investigations of the emergence and development of the micro-annulus generated by the cumulative plastic strain. A series of mechanical tests were conducted to quantify the stress–strain relationship and obtain the fundamental mechanical parameters of the set cement. A new full-size physical simulation experimental facility was built to identify the major controlling factor under cyclic loading–unloading. The experimental results demonstrated that a cumulative plastic strain was generated during the cyclic loading–unloading. Micro-annulus emerged in the first interface and became the pathway for gas migration. A set of three-dimensional numerical models was developed to analyze the micro-annulus emergence and development, considering the non-uniform in situ stress, fracturing pressure, and other actual geological parameters. Sensitivity analysis was conducted to analyze the variation in the micro-annulus in the horizontal, inclined, and vertical segments. The numerical results were consistent with the experimental results and demonstrated that decreasing the elastic modulus and increasing the Poisson's ratio, cohesive strength, and internal friction angle were beneficial for protecting the integrity of the cement sheath.