普光气田套管变形规律与强度评价方法

Deformation Law and Strength Evaluation Method of Casing in Puguang Gas Field

为了研究普光气田P110SS套管的变形规律及剩余强度评价方法,采用材料非线性和几何非线性模型,基于塑性失效准则,建立了套管-水泥环-地层有限元模型,同时通过现场测井数据对模型进行了验证。分析结果表明:普光气田套管变形主要是地震引发地应力的变化导致,套管变形呈椭圆状;水平地应力偏差越大,套管变形量及最大等效应力越大,且在水平地应力方向上套管的变形量达到最大;当地应力分布一定时,随着套管壁厚的增加,套管缩径量及最大等效应力先急剧减小,然后套管缩径量逐渐减小,套管等效应力基本不变,最后套管等效应力再次下降;套管变形量与套管最大等效应力间的关系同地应力组合形式无关,而是呈现出一定的规律性;采用多项式曲线拟合的方法建立了套管椭圆度与最大等效应力的数学方程,给出了变形套管剩余强度评价方法。所得结论可为普光气田套管变形井剩余强度评价提供理论依据。

To study the deformation law and residual strength evaluation method of P110 SS casing applied in Puguang gas field,the material nonlinearity and geometric nonlinear model are used to establish the casing-cement sheath-formation finite element model based on plastic failure criterion. The logging data are used to validate the model. The analysis results show that the casing deformation in Puguang Gas Field is mainly caused by the change of geostress caused by earthquake. The casing is deformed to elliptical shape. Greater horizontal geostress deviation results in larger casing deformation and maximum equivalent stress. The deformation of the casing in the horizontal geostress direction reaches the maximum. At a given geostress distribution,as the wall thickness of the casing increases,the casing diameter reduction and the maximum equivalent stress decrease sharply first,and then the casing diameter reduction decreases gradually,the casing equivalent stress is basically unchanged and then decreased again. The relationship between casing deformation and casing maximum equivalent stress if not related to the combination of geostress,but shows a certain regularity. The mathematical equation of the ellipticity and the maximum equivalent stress of the casing are established by the method of polynomial curve fitting. The residual strength evaluation method of the deformed casing is given. The study could provide a theoretical basis for the evaluation of residual strength of deformed casing in Puguang Gas Field.