Traditional prediction methods for formation integrity collapse pressure are difficult to describe for shale microfractures, joints, and weakness planes. In this study, for multiple weakness planes, a reasonable prediction model for shale wellbore collapse instability is constructed using the Mohr–Coulomb criterion and the multistructural plane strength theory, which can analyze the wellbore collapse pressure considering different weak planes. The results show that the collapse pressure increases with the increase in the number of weak planes. With an increase in the number of weak planes, the safe drilling window becomes narrower, which leads to an increase in the drilling difficulty. With the change in the drilling azimuth, the weak plane dip region where the maximum collapse pressure is located for different weak plane groups is transformed. For a weak plane group, the maximum collapse pressure changes from a dip angle of 30°–60° to 0° and 90° with the drilling azimuth. When the dip angle of two weak plane groups is 0°, the collapse pressure of the wellbore is the lowest, and the maximum collapse pressure changes from 60°–90° to 30°–60° with the change in drilling azimuth. When drilling along the minimum horizontal ground stress azimuth, there is only a difference when the included angle of inclination is 60°–180° and 240°–360°, and the other azimuth coincide, which indicates that the influence of the weak plane inclination on the collapse pressure is weakened when drilling along the azimuth. The effect of multiple weak planes on the collapse pressure is more significant in the later stages of drilling. The example analysis shows that under the action of multiple weak planes, the method can predict the formation collapse pressure more comprehensively and accurately than previous methods, which is meaningful in guiding drilling engineering in shale formations.

对于页岩微裂缝，节理和弱化面，很难描述传统的地层完整性坍塌压力预测方法。在这项研究中，对于多个弱平面，使用Mohr-Coulomb准则和多结构面强度理论构建了页岩井筒坍塌失稳的合理预测模型，该模型可以分析考虑不同弱面的井筒塌陷压力。结果表明，坍塌压力随着薄弱平面数量的增加而增加。随着弱平面数量的增加，安全钻孔窗口变窄，这导致钻孔难度增加。随着钻井方位角的变化，对不同的弱平面组最大崩塌压力所在的弱平面倾角区域进行了转换。对于一个弱平面组，最大倾覆压力随钻井方位角从30°–60°的倾角变为0°和90°。当两个弱平面组的倾角为0°时，井眼的坍塌压力最低，随着钻井方位角的变化，最大塌陷压力从60°–90°变为30°–60°。当沿着最小水平地面应力方位角钻孔时，只有当夹角为60°–180°和240°–360°时才存在差异，并且其他方位角重合，这表明弱平面倾斜的影响沿方位角钻探时，塌陷压力减弱。在钻井的后期阶段，多个弱平面对塌陷压力的影响更为显着。实例分析表明，在多个弱平面的作用下，