蠕变地层中含缺陷套管外挤压力分布的数值模拟

将蠕变地层视为粘弹性体,分别采用Maxwell粘弹性模型和线性强化弹塑性模型,建立了含缺陷套管—水泥环—蠕变地层有限元计算模型,旨在应用数值方法模拟在地质和工程因素及其联合作用下含缺陷套管外壁所受蠕动压力的分布规律,并对这类套管抗非均匀载荷的能力进行了有限元分析。采用逐步超松弛(SOR)迭代法进行了计算,为加快收敛速度,计算程序支持最佳松弛因子的自动快速搜索。算例分析表明,非均匀地应力条件下,最大地应力方向上套管外挤蠕动压力最小,而最小地应力方向上套管外挤蠕动压力最大;磨损缺陷改变了均匀载荷下套管外挤蠕动压力的分布规律,磨损处蠕动压力明显增大;与非均匀载荷相比,磨损是影响套管外蠕动压力分布更为敏感的因素。该数值结果可为复杂条件下含缺陷套管强度设计提供理论指导。

Numerical simulation of external pressure distribution of casing string with wear in creep formation

The creep formation was supposed to be viscoelastic materials.Both Maxwell viscoelasticity model and linear hardening elastic-plasticity model were used in this work,respectively.Thus,the analytical model of the assembled body including casing string with wear,cement sheath and creep formation was built based on finite element method(FEM).In order to illustrate the force distribution outside casings with wear,the numerical treatments of geologic,engineering-oriented factors and their combination were studied.And then the casings' resistant capacity to non-uniform loads was also evaluated.The computation program developed such a function as searching for the optimal iterative factor automatically to accelerate its convergence.Furthermore,the successive over relaxation method(SOR) was adopted to solve large-scale FEM equations.Some conclusions were conducted.The maximum external pressure is in the same direction with the minimum geostress and the opposite is also right.The pressure distribution outside casings is greatly changed by wear.The external pressure of the wear zone is obviously raised.So compared with the non-uniform geostress,the external pressure distribution is more sensitive to the wear in casing.These numerical results of the force distribution can be used to guide casing design.