Volume fracturing of shale gas wells has been observed to lead to the failure of cement sheath and to sustained casing pressure (SCP). This paper presents a new numerical investigation aimed at understanding the failure mechanism of the cement sheath during volume fracturing. A wellbore temperature model was established to obtain the required input parameters for the dynamic temperature boundary. The numerical model considers the coupling of casing, cement sheath, and formation rock to calculate the radial and tangential stresses in the cement sheath. In addition to the cement mechanical properties, the influencing factors considered include the casing pressure, fracturing fluid displacement, and initial temperature. The cement sheath integrity was evaluated using the Mohr-Coulomb failure criterion. The results show that the temperature of cement sheath changes drastically during fracturing. The radial and tangential stresses in the cement sheath change continuously with time. Lowering the internal wellbore pressure can effectively reduce the radial and tangential stresses in the cement sheath. Reducing the fracturing fluid displacement can significantly lower the radial and tangential stresses in the cement sheath. Increasing the initial fracturing fluid temperature will cause the radial stress of cement sheath to increase and the tangential stress to decrease. The use of cements with low Young's modulus values can significantly reduce the radial and tangential stresses in the cement sheath. The use of cements with low Poisson's ratio values can lower the tangential stress. The results obtained using the model were verified by field data that demonstrated no occurrence of casing pressure when using a cement with a low elastic modulus, as suggested by the model.

已观察到页岩气井的体积压裂导致水泥护套的破坏和持续的套管压力（SCP）。本文提出了一个新的数值研究方法，旨在了解水泥压裂过程中水泥护套的破坏机理。建立了井眼温度模型，以获得动态温度边界所需的输入参数。数值模型考虑了套管，水泥护套和地层岩石的耦合，以计算水泥护套中的径向和切向应力。除了水泥的机械​​性能外，所考虑的影响因素还包括套管压力，压裂液驱替量和初始温度。使用Mohr-Coulomb破坏准则评估了水泥护套的完整性。结果表明，在破裂过程中，水泥护套的温度发生了急剧变化。水泥护套中的径向和切向应力会随着时间连续变化。降低井眼内部压力可以有效减少水泥套管中的径向和切向应力。减少压裂液的排量可以显着降低水泥护套中的径向和切向应力。增加初始压裂液温度将导致水泥护套的径向应力增加而切向应力减小。使用低杨氏模量值的水泥可以显着降低水泥护套中的径向和切向应力。使用低泊松比值的水泥可以降低切向应力。