石油勘探地下套管损坏载荷强度设计研究

摘要

A finite element model of casing-cement-formation is established based on elastic-plastic mechanics theory and the data of oilfield,the casing stress distribution,deformation and residual intensity under the condition of different non-uniform load,wall thickness and steel grade are analyzed,and the measures of prevention and control under non-uniform load are studied.The results show that the maximum stress of casing rises with the increase of degree of loading's non-uniform and it is in the minimum horizontal principal stress direction.Furthermore,it generates (0.4 ～ 1) mm elliptical deformation in the non-uniform load,which weakens collapsing strength of casing.At last,there is (-9.0 ～ 75) MPa minimum residual intensity of N80 casing in the non-uniform load,but minimum residual intensity of P110 casing is (175 ～ 282) MPa in the same condition.It is the most effective measure of prevention and control casing damage of the non-uniform load.%套管在地层中多处于非均匀载荷之下,而非均匀载荷对套损影响甚大,在开采过程中,套管所受的非均匀载荷随着开采的进行而改变,设计的套管强度可能无法满足要求.针对上述问题,以弹塑性力学和现场数据为基础,建立了套管-水泥环-地层有限元模型,研究在不同的非均匀载荷、壁厚、钢级下套管的应力分布、变形大小、剩余强度等,从而研究非均匀地层载荷下套损的防控措施.研究表明:套管的最大应力随非均匀程度的增加而增大,且最大应力在最小水平主应力方向;在非均匀载荷作用下套管发生了(0.4-1)mm的椭圆变形,削弱了套管的抗挤能力;采用N80钢级的套管在不同的非均匀载荷下,最小剩余强度为(-9.0-75)MPa,而采用P110钢级套管其最小剩余强度为(175-282) MPa,因此提高钢级能有效防控非均匀地层的套损.