非均匀载荷下套管强度的计算

CALCULATION OF CASING STRENGTH UNDER NONUNIFORM LOADING

在建立了泥岩蠕变非均匀外载模型基础上，提出了一种对泥岩蠕变引起的椭圆形非均匀外载下套管应力和强度的计算方法。在非均匀载荷下，套管所能承受的最大载荷迅速降低。当内压为０．１ＭＰａ时，套管的临界载荷平均约为均载情况下的１１％。大庆榆树林油田泥岩段的套损分析表明高压注入水沿垂直裂缝进入泥岩层，引起泥岩层吸水蠕变，使得所用Ｊ－５５套管难以承受较大的非均匀挤压力，导致套管损环。建议在易发生泥岩蠕变井段，应采用Ｐ－１１０型套管以确保井筒安全。

Calculation methods of casing stress and strength under nonuniform loading distributed as ellipse induced by mudstone creep are derived on the basis of establishing nonuniform outside loading models for mudstone creep. On the condition of nonuniform loading,maximum loading that the casing can bear is reduced rapidly.When innerpressure is 0.1MPa,critical loading of the casing is about 11 percent, on the uniformed of loading condition averagely.Analysis of the casing deformation at mudstone formation in Daqing Yushulin oil field showed that the flooding water with high pressure entered into mudstone formations along vertical fractures caused the mudstone formation to absorb water to creep,and made J55 casing difficult to bear larger nonuniform squeezing pressure and leaded to casing deformation.To ensure the safety of the wellbore,it is proposed that P110 casing is used in the section which the mudstone creep is easily occured.