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首页> 外文期刊>Journal of natural gas science and engineering >A theoretical study of the critical external pressure for casing collapse
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A theoretical study of the critical external pressure for casing collapse

机译：套管坍塌临界外压的理论研究

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A new theoretical casing collapse model is proposed on the basis of a refined reduced modulus calculation method. The reduced modulus of considers the co-existence of the elastic and plastic regions on the casing cross section. The collapse pressure for an ideal circular casing is expressed as a weighted harmonic sum of the critical elastic pressure and casing yielding pressure. Three kinds of casing imperfections including the wall thickness variation, ovality and non-uniform external pressure on casing collapse are further considered to amend the ideal casing collapse model. The equivalent wall thickness due to wall thickness variation is introduced, and the critical elastic pressure and yielding pressure under the effects of initial ovality and non-uniform external pressure are obtained. On this basis, the collapse pressure for an oval casing with thickness variation under non-uniform external pressure is obtained with superposition principle. The effects of axial force, bending moment and torque on collapse pressure are included with the reduced yielding point. All the above factors are integrated into a unified casing collapse model. At last, the comparison between the new model and API specification is further discussed. The results indicate that the new model gives a more sophisticated description of casing collapse problem. Introducing the casing imperfections improves the consistency between the theoretical and experimental results at the transition between elastic and plastic ranges. The non-uniform external pressure plays the most important role in the casing collapse problem. The existence of non-uniform external pressure, axial force, bending moment and torque also reduces the critical casing collapse pressure a lot. (C) 2015 Elsevier B.V. All rights reserved.
机译：在改进的降模量计算方法的基础上，提出了一种新的理论套管破坏模型。减小的模量考虑了套管横截面上弹性区域和塑性区域的共存。理想圆形套管的坍塌压力表示为临界弹性压力和套管屈服压力的加权谐波和。进一步考虑了壁厚变化，椭圆度和套管坍塌外压不均匀三种套管缺陷，以修正理想的套管塌陷模型。引入了由于壁厚变化引起的等效壁厚，并获得了初始椭圆度和非均匀外压作用下的临界弹性压力和屈服压力。在此基础上，利用叠加原理求得了椭圆形壳体在不均匀外压作用下厚度发生变化的坍塌压力。屈服点降低包括轴向力，弯矩和扭矩对破坏压力的影响。上述所有因素都整合到统一的套管塌陷模型中。最后，进一步讨论了新模型与API规范之间的比较。结果表明，新模型对套管塌陷问题给出了更为复杂的描述。引入套管缺陷可改善弹性和塑性范围之间过渡处的理论结果与实验结果之间的一致性。外部压力不均匀在套管坍塌问题中起着最重要的作用。不均匀的外部压力，轴向力，弯矩和扭矩的存在也大大降低了关键的套管塌陷压力。 （C）2015 Elsevier B.V.保留所有权利。

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