Abstract: The analytical solutions for stress and displacement around a borehole during drilling were given. On the base of the solutions, the balance path curve for pressure and displacement at the face of the wellbore was drawn. The conclusion is that wellbore collapse is an instability phenomenon of extreme point type, and a number of issues in oil industry are clarified. At last, the formula of critical pressure for wellbore collapse is derived, and the condition for air and gas drilling is analyzed.

Key words: stability, wellbore failure, wellbore collapse, method of initial stress

摘要： 给出了钻井过程井壁围岩的应力场和位移场的解析解。在此基础上，建立了井壁压力和井壁位移的平衡路径曲线，提出井壁坍塌是一种极值点型失稳现象，澄清了石油工程中的一些问题。得到了井壁失稳的临界压力公式，并给出了气体钻井的适用条件。

关键词: 稳定性, 井壁破坏, 井壁坍塌, 初应力提法