Distribution Characteristics and Cause Analysis of Casing Deformation during Hydraulic Fracturing of Shale Gas Wells

The distribution characteristics and causes of casing deformation during hydraulic fracturing were investigated. Finite element models of a casing-cement sheath-formation assembly, considering a multi-stage fracturing process, were established. The axial displacement law of formation during multi-stage fracturing was analyzed. Furthermore, considering the existence of faults, the mechanism of casing deformation caused by fault slippage due to axial displacement was analyzed. Finally, the influence of fault parameters, as well as the casing's geometry and mechanical parameters, on casing deformation were clarified. The results show that the casing deformation point is densely located near landing point A and sparsely located near toe point C. The entry of high-pressure fracturing fluid into the formation would reduce the effective stress of the formation and could even change it from compression to tension, which would mean that the formation in the fractured section would be stretched in the axial direction, squeezing the formation in the non-fractured area and causing axial displacement; the closer the formation is to point A, the greater the displacement. The change in casing deformation can be divided into three stages. In the first, the casing deformation is zero when the fracturing section is far from the fault. In the second, the casing deformation increases significantly when the fracturing section is close to the fault. In the third, the casing deformation increases slowly when the fracturing section deviates from the fault. The closer the fault is to landing point A, the greater the length, the smaller the dip angle, and the larger the casing deformation, and vice versa. In contrast, increasing casing wall thickness and steel grade has little effect on relieving the casing deformation.