非均匀外载下弯曲井眼中含缺陷套管抗挤强度计算新模型

A new model for calculating the collapsing strength of defective casing under non-uniform loads in curved borehole

目前套管抗挤强度通常按照ISO 10400标准计算,但该标准在计算时将斜井视为直井,未考虑井眼弯曲的影响。虽然已有学者建立了考虑井眼弯曲后的套管抗挤强度计算公式,但其公式未考虑套管制造缺陷如不圆度、壁厚不均的影响,不符合实际情况。为了建立综合考虑各项影响因素的套管抗挤强度计算公式,将井眼弯曲、制造缺陷考虑在内,建立了套管抗挤强度计算新模型。研究结果表明:①新建模型考虑了套管所受非均匀外载、井眼弯曲、制造缺陷对抗挤强度的影响,更符合井下套管实际情况;②通过对比得出自建公式计算出的抗挤强度值变化趋势与黄根炉教授建立的弯曲井眼套管抗挤强度公式计算值、ISO公式计算值的变化趋势一致;③通过有限元软件建立了弯曲井眼套管三维模型,将模拟值分别与自建公式计算值、黄根炉教授建立的套管抗挤强度公式计算值、ISO公式计算值进行对比,自建的公式计算值更接近有限元模拟值;④计算值变化趋势及其与模拟值的对比能反映出新模型的正确性及计算精度,可以为井下套管抗挤强度的精确计算提供参考。

The current casing collapsing strength is usually calculated according to ISO10400 standard.However,this standard treats deviated wells as vertical ones without considering an influence of curved borehole.Some scholars have established formulas for calculating this strength while considering the curved borehole,but the formulas don't include manufacturing defective of casing,e.g.out of roundness and uneven wall thickness.So,it cannot reflect true situation accurately.In order to develop another formula with full consideration on various influencing factors,this study established a new model for calculating the collapsing strength of casing which includes curved borehole and manufacturing defective.Results show that(1)the new model considers the effects of non-uniform load,curved borehole,and manufacturing defective on the collapsing strength,so it can reflect the actual downhole casing more accurately;(2)comparison results also present that the change trend of collapsing strength calculated by this new formula is in accordance with that from one formula developed by Professor Huang Genlu with consideration on the influence of curved borehole and another ISO formula;(3)a 3D model of casing in curved borehole is established by means of finite element software.Both simulation and calculation comparison among the new formula,and the Professor Huang Genlu and the ISO formulas indicate that the result from the first one is closer to the finite-element simula⁃tion;and(4)for the calculation result from the newly established model,its change trend and comparison with the simulation result can reflect higher accuracy and precise.These may provide reference for accurately calculating the collapsing strength of downhole casing.