深水顶张力隔水管钻井作业时的非线性振动特性分析

NONLINEAR VIBRATION ANALYSIS OF DEEPWATER TOP TENSION RISER UNDER DRILLING CONDITION

隔水管是深水钻井过程中的薄弱环节,其横向振动可能引起偏磨、塌陷、断裂等多种失效形式,研究深水隔水管的横向振动特性,可为深水钻井参数选择和钻完井施工设计提供理论依据,提高隔水管的安全可靠性.将深水隔水管简化成Euler-Bernoulli梁,引入大变形应变-位移方程和弹簧边界条件,利用Hamilton原理建立了波流耦合作用下深水隔水管的运动模型,得到了作业工况时隔水管横向振动的非线性动力学方程,Galerkin离散后,通过数值分析方法研究了深水隔水管的振动稳定性机理.分析结果表明,系统的主共振存在多值和跳跃现象,随着隔水管直径与壁厚之间比值D/τ的增大,系统频响振幅逐渐增大;波浪高度与波浪周期比值H/T增大,幅频响应的带宽逐渐增加,不稳定区域逐渐增大;隔水管长度与波浪有效高度的比值l/H会使主共振跳跃幅值明显增大.波浪周期从3~10s变化时,深水隔水管系统经历着周期运动与混沌运动的交替变化,存在倍周期窗口并具有明显的分叉现象.

Riser is a weak point during deepwater drilling process,and its transverse vibration will lead to various failures such as eccentric wear,breakdown and collapsing,et al. The study of transverse vibration lays on a theoretical foundation for the choice of deepwater drilling parameters and design for well drilling and completion, which will increase the security of risers. In this paper, the deepwater riser is simplified as a Euler-Bernoulli beam with large deformation strain-displacement equation and elastic boundary condition, and a mathematic model is deduced for the deepwater riser under coupling force of wave and current by using Hamilton′s principle. The nonlinear dynamic equation describes the transverse vibration of deepwater riser under drilling condition. Galerkin method and numerical analysis are then used to find out the stability mechanism of transverse vibration. The analysis above shows that the multiple values and jump phenomenon exist in the main resonance process. The response amplitude raises when the ratio D/τ between diameter and thickness of the riser increases. The bandwidth broadens and unsteady region extends as the ratio H/T between wave effective height and period increases. The response amplitude of jump phenomenon becomes more obvious with the increase of ratio l/H between riser length and wave height. The deepwater riser system experiences alternate change of periodic motion and chaotic movement when the wave period varies from 3s to 10s,and simultaneously,there are evident period-doubling bifurcation windows.