Study on the Mechanism and Influencing Factors of Casing Deformation Caused by Shale Slippage

Casing deformation can obstruct downhole tools from reaching the target depth, disrupt normal operations, and even render some wells inoperative, posing a major challenge to the development of deep shale gas reservoirs. This study explores the mechanism of casing deformation (CD) caused by formation slip during hydraulic fracturing in deep shale gas wells through theoretical analysis and numerical simulation. Based on this analysis, a three-dimensional finite-element model of the formation-cement sheath-casing system is constructed, using lateral displacement as a quantitative measure to assess the extent of CD in horizontal shale gas wells. The results reveal that increasing the casing wall thickness and steel grade improves the casing’s shear resistance; however, deformation still occurs under formation-induced shear stress. When the elastic modulus of the cement sheath decreases from 40 to 0 GPa, the maximum lateral displacement of the casing is reduced by 79.83%. Additionally, the Mises stress of the casing increases with Poisson’s ratio, although its effect is relatively minor. The severity of CD increases with the angle between the casing axis and natural fractures, reaching its maximum when the angle is 90°. This study offers theoretical insights and practical approaches to maintaining casing integrity and mitigating CD in deep shale gas wells under hydraulic fracturing conditions.