极端条件下气井油管柱振动力学行为的有限元分析

Finite Element Analysis for Vibration Mechanical Behavior of Tubing String in Gas Wells under Extreme Conditions

为了系统地、定量地分析极端条件下气井油管柱振动力学行为,根据新疆某油田油管柱结构尺寸,基于有限元法,建立了两种结构带封隔器的极端条件气井油管柱振动有限元力学模型,编写了极端条件下气井油管柱的振动动力学行为分析的APDL有限元程序,对该极端条件下气井管柱振动问题开展了系统分析和研究。研究表明:①对比改进前后管柱结构的前15阶模态和频率,改进后油管柱均有利于减缓振动对油管柱的损伤;②在瞬态动力响应方面,改进后的结构对事故高发(4200~5500 m)油管段内平均应力降低了约104 MPa,同时中和点也下移了231 m,均有利于提高极端条件下气井油管柱安全性及其疲劳寿命。结论表明,建立的模型可分析油管柱的振型,固有频率以及随时间历程变化的应力、速度、位移等,为极端条件下气井油管柱疲劳寿命预测、中和点变化以及油管柱在采气期间的振动力学机理提供定量的数据,同时为新井管柱设计提供了理论依据。

In order to systematically and quantitatively analyze the vibration mechanical behavior of tubing string in gas wells under extreme conditions,two finite element mechanical models were established according to the tubing string structures and sizes of an oilfield in Xinjiang for the vibration of tubing string with packers under the said conditions using finite element method.APDL finite element program was compiled,by which the vibration problems of such tubing string were systematically analyzed and studied.Study findings show that①After comparing the first 15th modes and frequencies of two string structures,it was found that the improved structure could mitigate the damage of vibration to tubing string.②In respect of transient dynamic response,the improved structure made the average stress in high-risk string section(4200-5500 m)reduce by about 104 MPa,and the neutral point moved down by 231 m,which are conducive to improving the safety and fatigue life of string.It is concluded that the established model can be used to analyze the string vibration mode,inherent frequency,and stress,velocity and displacement that change with time,providing quantitative basis for the fatigue life prediction,neutral point change and vibration mechanical mechanism of tubing string in gas wells under extreme conditions,as well as theoretical basis for tubing string design of new wells.