稠油热采井套管的预应力分析

以暴露于热蒸汽中的目的层套管为研究对象,根据弹性力学理论,首先给出了套管在热应力和非均匀地应力作用下的三轴应力表达式,然后利用对套管施加预应力来降低套管的轴向热应力,使得套管的有效应力控制在相应温度下套管的最小屈服极限内为原则,得到了热采井套管三轴预应力设计方法,并对辽河油田常用的N80钢级套管进行了预应力设计分析,给出了该套管在不同注汽温度和井深条件下所应使用的径厚比及相应的预应力值。研究表明,拉预应力在一定范围内有利于提高套管的安全性,传统的单轴预应力设计方法具有明显的缺陷,建议以后稠油热采井在进行预应力设计时应考虑热应力和实际非均匀地应力的共同作用,以及油层出砂对套管产生的影响。

Prestress analysis of casing strings in heavy oil thermal production wells

Based on the elastic theory,this paper derived the triaxial stress formulas of casing exposed to heating steam under thermal stress and non-uniform geologic stress,and established a new method to design the prestress of casing.The casing's effective stress should be under the minimum yield.Through analyzing the prestress design of N80 casing which was often used in Liaohe Oilfield,this paper also gave the ratio of diameter to wall thickness and the corresponding prestress of N80 casing at different steam injection temperature and well depths.The study manifests that the safeness of casing can be enhanced by pulling up prestress properly and the conventional uniaxial prestress design has evident defects.As thermal stress,non-uniform geologic stress and effect of sand production on stress are considered in triaxial prestress design,it is suggested that triaxial prestress design is adopted in heavy oil thermal production wells.