套管钻井中套管柱疲劳可靠性及相关力学特性研究

利用CAE仿真技术和可靠性疲劳实验方法,研究了套管钻井中的有关力学问题.分析了不同径厚比套管的受力状态、磨损套管剩余强度、套管柱的振动模态和疲劳可靠度.研究结果表明,径厚比越大,套管管体Mises应力越大,套管发生失稳的临界荷载越小.对于均匀磨损,随着磨损长度的增大,套管的剩余抗拉和抗扭强度逐渐变大,并达到一个极限值;对于非均匀磨损,其剩余抗拉强度与磨损长度之间的关系均近似服从指数分布.两种磨损状态下,套管柱剩余抗拉和抗扭强度都随磨损量的增加而降低;套管柱外径对套管横向振动固有频率的影响大于径厚比对其的影响,纵向固有频率主要取决于管柱长度.运用可靠性方法,基于概率分析设计了单轴和双轴疲劳可靠性试验,得到了套管柱的单轴和双轴概率疲劳特性,推导出套管钻井的P-S-N曲线方程.

Analysis on mechanics and fatigue reliability of casing string during casing drilling

The mechanics in the process of casing drilling were analyzed using the CAE stimulation and tests of fatigue reliability, including the force acted on the casing with different diameter-thickness ratio, residual intensity of worn casing, vibration modal and fatigue reliability of the casing string. The study results showed that the Mises stress on the casing had a proportional relation with the diameter-thickness ratio, and the critical instability load of casing had a reverse proportion with the diameter-thickness ratio. For the uniform wear of casing, the longer of the wear length of casing led to the bigger residual intensity and resistance to distortion, which finally reached a limit value. For the non-uniform wear of casing, the residual intensity had an exponential relation with the wear length. The residual intensities both the uniform wear and non-uniform wear of casings have the reverse proportions with the abrasion depth on casings. The external diameter of casing had the more influence on lateral vibration inherent frequency than the diameter-thickness ratio. The length of casing string controlled the lateral vibration inherent frequency. The reliability tests both the axial fatigue and the biaxial fatigue of casing strings were designed by means of examination and numerical simulation, and the P-S-N curves were obtained.