Abstract In this paper, the poroelastodynamic theory is employed to study the transient failure of a suddenly excavated borehole in a poroelastic continuum subjected to a non-hydrostatic far-field stress state. By introducing four scalar potential functions, the solutions for the stresses and pore pressure are given as the product of an exact treatment of the full fluid-solid coupling through field expansions with emphasis on the effect of solid-fluid acceleration. Transient tensile and shear failure responses are investigated based on an overbalanced drilling for two types of boundary conditions: a permeable surface and an impermeable surface. It's found that the permeable borehole has a larger tensile failure area than the impermeable borehole in the direction of maximum in-situ stress, and meanwhile, four symmetric shear failure areas are observed near the borehole for both internal boundary conditions. Influences of poroelastic parameters on the transient failure responses of a permeable borehole are analyzed in a detailed parametric study. The failure responses for both classical quasi-static poroelastic and poroelastodynamic theories are computed and compared to study the importance of the inertial effect in very early times. Noteworthy is that the borehole is more unstable in the poroelastodynamic theory compared to the classical poroelastic theory because the inertial effect enhances the transient response in the early times, increasing the minimum principal stress to a tensile state in the direction of maximum in-situ stress so as to result in transient generation of both tensile and shear failures in that direction. The results in this paper provide fundamental insights on the borehole instability under some dynamic bottom-hole conditions.

中文翻译：

---

多孔弹性连续体中钻孔的瞬态破坏

摘要 本文利用多孔弹性动力学理论研究了多孔弹性连续体中突然开挖的钻孔在非静水力远场应力状态下的瞬态破坏。通过引入四个标量势函数，应力和孔隙压力的解是通过场扩展对全流固耦合进行精确处理的产物，重点是固流加速的影响。瞬态拉伸和剪切破坏响应基于两种类型的边界条件的过平衡钻孔：渗透表面和非渗透表面。发现在最大地应力方向上，可渗透钻孔比不渗透钻孔具有更大的拉伸破坏面积，同时，对于两种内部边界条件，在钻孔附近观察到四个对称的剪切破坏区域。在详细的参数研究中分析了多孔弹性参数对可渗透钻孔的瞬态破坏响应的影响。计算经典准静态多孔弹性理论和多孔弹性动力学理论的失效响应并进行比较，以研究早期惯性效应的重要性。值得注意的是，与经典的多孔弹性理论相比，孔弹性理论中的钻孔更不稳定，因为惯性效应增强了早期的瞬态响应，将最小主应力增加到最大地应力方向上的拉伸状态，因此从而导致在该方向上瞬时产生拉伸和剪切破坏。