Failure mechanism and control method of casing shear deformation induced by fault slip during multi-stage fracturing

During shale gas development, multi-stage fracturing-triggered fault movement was the dominant cause of casing shear failure, which significantly compromises well productivity. To address this, numerical models of formation-cement sheath-casing and formation-cement sheath-rubber-casing under fault slip conditions during multi-stage fracturing were established in this study. The study systematically investigated the deformation mechanisms and corresponding mitigation measures for wellbore assemblies under fault slip. The model’s reliability was verified through experiments. The effects of rubber sheath thickness and rubber material on casing shear deformation were quantitatively analyzed. The results indicated that fault slip led to localized stress concentration, which caused a reduction in casing diameter and prevented bridge plugs from passing through. However, incorporating a rubber sheath alleviated casing shear deformation, controlled the reduction in casing diameter, and usually allowed bridge plugs to pass. The study further analyzed the influence of fault slip distance, fault dip angle, rubber sheath thickness, and rubber material on casing diameter. Numerical simulations revealed that greater fault slip distances, smaller fault dip angles, and thinner rubber sheaths caused more severe casing deformation, whereas changing the rubber material had minimal influence on casing diameter. The research results can provide theoretical insights and engineering references for optimizing the parameters of tools designed to address casing shear deformation.