Mechanism and Control of Casing Deformation under Strike-Slip Fault Movement in Shale Gas Reservoirs

Summary The effective development of shale gas is severely hampered by casing shear deformation issues, which commonly arise during the hydraulic-fracturing process. However, the actual morphology of such deformation and its relationship with fault-slip displacement remain poorly understood. To address this, we investigated casing shear deformation morphology and the variation of casing inner diameter under varying slip displacements by means of experiments and micro-computed tomography (CT) analysis. Experimental results were used to validate the reliability of our numerical simulation methodology. Subsequently, field-scale numerical simulations were performed to examine the influence of strike-slip faults with various orientations on casing cross-sectional shape and inner diameter. Our findings indicate that casing deformation severity is jointly determined by the fault-wellbore intersection angle in the slip direction and the fault-slip displacement. Based on this relationship, we derived a calculation formula for inner-diameter reduction to quantify casing deformation. The study also examined how different sensitivity factors affected the casing inner-diameter reduction and strain. Finally, by integrating fault-slip theory with the casing deformation formula, we proposed wellbore layout measures: avoiding long faults, avoiding faults with high-risk angles, and maintaining distance from fault centers. Additionally, controlling and preventing casing deformation effectively requires reducing fluid pressure on the fault during fracturing operations.