Failure evaluation mechanism of cement sheath sealing integrity under casing eccentricity during multistage fracturing

作者：Yan Xi, Yu Yao, Xueli Guo, Jun Li, Yu-Dong Tian, Gong-Hui Liu · 发表于：Petroleum Science · 年份：2024 · DOI：10.1016/j.petsci.2024.04.013 · 被引用次数：20 · 研究领域：Drilling and Well Engineering、Tunneling and Rock Mechanics、Rock Mechanics and Modeling

A microannulus (MA) is the primary reason for sustained casing pressure in multi-stage fractured-shale gas wells. However, the effect of the casing eccentricity on the long horizontal section has not been considered. In this study, a full-scale integrity tester for cement sheaths is adopted to measure the cumulative plastic deformation. Numerical models are applied to evaluate the development of the cumulative plastic deformation and quantify the MA width considering casing centralization and eccentricity in the context of multiple loading and unloading cycles. Subsequently, the influences of the eccentricity distance and angle, cement-sheath mechanical variables, and different well depths on the cumulative sheath plastic deformation and sheath MA development are explored. The research results demonstrate that casing eccentricity significantly increases the cumulative sheath plastic deformation compared with that of the casing-centered condition. Consequently, the risk of sealing integrity failure increases. The accumulated plastic deformation increases when the eccentricity distance increases. In contrast, the initial plastic deformation increases as the eccentricity angle increases. However, the cumulative plastic deformation decreases after a specific loading and unloading cycle count. Affected by the coupled influence of the internal casing pressure and fracturing stages, the width of the MA in the horizontal section increased from the toe to the heel, and the casing ecce...