<p>This study investigates shear deformation of the casing during shale gas well fracturing through mechanical analysis and deformation calculations. We evaluated casing deformation induced by natural fracture shear slip, critical slip activation conditions, and key factors governing casing shear stress and deformation. The results demonstrate that elevated fluid pressure within natural fractures increases both the shear stress on the casing and the range of fracture approach angles favorable for shear activation. Consequently, this elevates the likelihood of shear-activated fractures and the associated risk of casing shear deformation. And maximum shear stress occurs within fracture approach angles of 30–45° and their supplementary range. For wellbores intersecting well-developed natural fractures, maintaining fluid pressure below the critical shear strength threshold during hydraulic fracturing operations mitigates casing deformation risks by preventing induced shear slip. Shear stress of the casing is positively correlated with horizontal in situ stress difference, natural fracture length, and the Young’s modulus and Poisson’s ratio of the cement sheath and casing. Conversely, it is negatively correlated with the Young's modulus and Poisson's ratio of the formation rock, the friction coefficient, and casing wall thickness. Variations in the Young's modulus and Poisson's ratio of the casing material itself exhibit minimal impact on casing shear stress. Using cement possessing a low Young’s modulus and a low Poisson’s ratio for well cementation effectively mitigates casing shear failure. Higher Young’s modulus and Poisson’s ratio values in the formation rock result in reduced casing deformation displacement. Conversely, greater horizontal in situ stress differences and longer natural fracture lengths increase deformation displacement. Within the fracture approach angle range of 0–180°, casing shear deformation exhibits a bimodal distribution, with maxima occurring within the 30–60° range and its supplementary angular interval. Geo-mechanical instability induced by in situ stresses within naturally fractured shale reservoirs constitutes the primary cause of casing deformation. At direct intersections between well trajectories and natural fractures, maintaining a distance from the fracture central zone is advised to minimize induced shear displacement. These findings provide a theoretical foundation for understanding casing shear failure stress-deformation characteristics, elucidating governing mechanisms, and guiding deformation prevention and control strategies.</p>