The tubing used in a gas well rarely collapses and fails during applying annulus pressure. In this study, the failure causes of tubing collapse were analyzed by means of data verification, macroscopic observation, magnetic particle inspection, physical and chemical inspection, optical microscopy, and tubing collapse test. Mechanical analysis of the string and full-scale physical simulation test simulating downhole working conditions. Finally, the verification analysis of the collapse test is carried out by the finite element analysis (FEA). The results showed that (1) the physical dimension, physical and chemical properties, and collapse resistance of this batch of tubing met the requirements of the tubing ordering technical standard. (2) Assuming that the well packer slip was unsealed and could slide freely, the mechanical theoretical analysis of collapsed tubing string and collapse test under simulated working condition load was carried out, which reproduced the load when the tubing collapsed. It can be seen from this that the packer did fail. (3) The FEA calculation results showed that when the external pressure was greater than 30.75 MPa, it would inevitably lead to collapse failure in case of packer unsealed. In conclusion, the root cause for the collapse failure of the 105th underground tubing string was that the packer lost its sealing function, resulting in an abnormal axial load. While under the action of external pressure, the tubing was overloaded and collapsed. It is recommended to carry out verification tests on the material performance of packer slip, the dimensional changes of packer tool outer diameter and inner diameter under actual well conditions, the creep behavior of packer seal, and the performance of shear pin under actual working conditions, especially in the well containing H₂S, so as to prevent the pressure leakage of gas well annulus caused by packer unsealing and the reoccurrence of such downhole string collapse accidents. The first collapse test under simulated working condition load is conducted in this paper. Analyzing the collapse failure work and putting forward suggestions to effectively prevent similar failures from happening again are of great significance to the oilfield.

中文翻译：

---

某气井油管塌陷失效分析

气井中使用的管道在施加环空压力期间很少发生塌陷和失效。本研究通过数据验证、宏观观察、磁粉探伤、理化检验、光学显微镜、油管塌陷试验等手段，对油管塌陷失效原因进行了分析。管柱力学分析和模拟井下工况的全尺寸物理模拟试验。最后通过有限元分析（FEA）对倒塌试验进行验证分析。结果表明：（1）该批管材的物理尺寸、理化性能、抗挤毁性能均符合管材订购技术标准的要求。(2)假设封隔器卡瓦未密封且可自由滑动，进行了管柱塌陷力学理论分析和模拟工况载荷下的塌陷试验，再现了油管塌陷时的载荷。从这里可以看出，加壳器确实失败了。(3)有限元计算结果表明，当外压大于30.75 MPa时，封隔器在未密封的情况下，必然导致塌陷破坏。综上所述，105号地下管柱塌陷失效的根本原因是封隔器失去密封功能，产生异常轴向载荷。而在外压作用下，油管超载而塌陷。建议对封隔器卡瓦的材料性能、封隔器工具外径和内径在实际井况下的尺寸变化、封隔器密封件的蠕变行为、剪切销在实际工况下的性能进行验证试验，特别是在含H ₂ S井中，防止因封隔器开封造成气井环空压力泄漏以及井下管柱塌陷事故的再次发生。本文进行了首次模拟工况荷载下的倒塌试验。分析垮塌故障工作并提出建议，有效防止类似故障再次发生，对油田具有重要意义。