非均匀外压下含磨损缺陷套管的挤毁极限载荷分析

采用非线性有限元方法，按平面应变问题处理，分析了含磨损套管受井下非均匀外压作用时的挤毁极限载荷及挤毁失效方式，同时计算了含磨损套管受均匀外压作用时的挤毁极限载荷，与试验结果比较吻合。研究结果表明，套管在均匀外压下发生挤毁时，极限载荷最大，挤毁模式是套管磨损部位的管壁向管外凸出，屈服区主要分布在套管塌陷部位外壁及磨损部位的内壁。非均匀外压下发生挤毁时，挤毁模式是套管磨损部位的管壁向管内方向塌陷，屈服区域主要分布在套管挤毁后凸出部位内外壁及塌陷部位的内外壁。且外压分布越不均匀，挤毁极限载荷越低；套管偏心度越大，抗挤能力越差。

On Calculating Critical Collapse Load of Petroleum Casing with Both Wear and Non-Uniformity in Pressure Considered

API(American Petroleum Institute) did not include the effect of wear and non-uniformity in pressure in its calculation formulas for critical collapse load of petroleum casing . In our experience, we sensed the need for considering this effect. Section 1 gives Fig.1 as the FEM(finite element method) model for our calculation. Sections 2 and 3 use well known FEM technique to derive formulas needed in our calculations. Section 4 gives and analyzes calculated results. Fig.5 shows the significant effect of non-uniformity in pressure on decreasing critical collapse load and Fig.6 shows the significant effect of wear on decreasing critical collapse load. Fig.4 shows the comparison of collapse patterns under uniform pressure and non-uniform pressure respectively. In Fig.4(a) for petroleum casing under non-uniform pressure, the wear-damaged area is of concave shape. In Fig4.(b) for petroleum casing under uniform pressure, the wear-damaged area is of convex shape.