典型工况下完井管柱伸缩管力学分析及安全性评价

Mechanical analysis and safety evaluation on telescopic tube contained in completion string under typical working conditions

为减小深井超深井管柱轴向拉力,降低安全系数,常需要在管柱中配置伸缩管,但在进行管柱强度校核时伸缩管处常会出现安全系数突变,由于对其本体缺少力学分析方法,无法对管柱安全作出准确判断,影响试油完井管柱的安全性。应用有限元分析软件建立伸缩管全尺寸有限元模型,分析了坐封、射孔、压裂、开井、关井工况下和极端工况下伸缩管的载荷及应力,给出了5种典型工况对应的极端工况下的伸缩管最大载荷。依据拉梅公式和强度理论,推导得到在复杂载荷下的伸缩管强度计算方法,求得在典型和极端工况下的伸缩管应力值。结果表明:在深井超深井中,压裂工况下伸缩管应力值最高,是最不利工况;坐封、射孔、开井、关井工况下,伸缩管的安全系数通常在1.35以上。得到了5种典型工况对应的极端工况下伸缩管内外压和轴向力组合,提供了实际施工应避免的载荷组合模板。理论分析无法考虑伸缩管键槽的存在,也无法考虑应力集中的影响,理论分析得到的应力较数值分析低15%左右。建立的典型工况下伸缩管的安全评价方法为伸缩管及其对管柱的安全影响分析提供了理论支持。

In order to reduce the axial tensile force on the pipe string in deep and ultra-deep wells,and to reduce safety factor,it is often necessary to configure a telescopic tube in the pipe string.However,when checking the strength of the pipe string,the safety factor of the pipe string often occurs abrupt change.Due to the lack of mechanical analysis methods for the pipe string,it is impossible to make an accurate judgment on the safety of the pipe string,which affects the safety of the completion pipe string for oil testing.The full-scale finite element model of the telescopic tube was established by using the finite element analysis software,and the loads and stresses on the telescopic tube under working conditions,such as setting,perforation,fracturing,well opening,and well shut-in,and extreme conditions were analyzed.And the maximum load on the telescopic tube under extreme conditions corresponding to five typical working conditions was given.According to Lame equation and strength theory,the method for calculating the strength of the telescopic tube under complex load was derived,and the stress value of the telescopic tube under typical and extreme conditions was calculated.The results show that:in deep and ultra-deep wells,the stress value of the telescopic tube is the highest under fracturing condition,which is the most unfavorable condition;while under the conditions of setting,perforation,well opening and well shut-in,the safety factor of the telescopic tube is usually above 1.35.The combination of internal,external force and axial force on the telescopic tube under extreme working conditions corresponding to five typical working conditions was obtained,which provides a load combination template that should be avoided in actual operation.The theoretical analysis cannot take into account the existence of the keyway of the telescopic tube,nor the influence of stress concentration.The stress obtained by the theoretical analysis is about15%lower than that of the numerical analysis.The established safety evaluation method for telescopic tube under typical working conditions may provide a theoretical support when analyzing the safety effects of telescopic tube on pipe strings.