软弱夹层对深水采油管柱地震反应的影响

Influence of soft interlayer on seismic response of casing string for deepwater production

海底泥线以下分布的软弱夹层对深水采油管柱井身结构的稳定性有着重要影响,尤其当地震发生时,会在土层交界面处管柱截面产生很大的弯矩和剪力。依据桩基的动力响应理论,引入回传射线矩阵法,建立了适于深水采油管柱的地震响应分析模型。模型中将组合套管柱等效为变截面Timoshenko梁,分别从软弱夹层的厚度和剪切波速分析,探讨了套管柱在各土层交界面处弯矩和剪力幅值的变化规律。结果表明,当软弱夹层的剪切波速减小,或厚度趋向临界值hcr时,都会导致夹层界面处套管柱的弯矩和剪力幅值的增大。因此,海洋工程中在钻遇软弱夹层时须充分考虑其对套管柱地震反应的影响。

The soft interlayer under seafloor has great influence on the stability of subsea casing string for deepwater production.Especially,the earthquakes can cause a great bending moment and large shear force on the cross-section of casing string.An analytical model for the seismic response of subsea casing string is established on the basis of pile foundation theories and method of reverberation-ray matrix.The casing string is assumed to be a Timoshenko beam of variable cross-section.The bending moments and shear forces of different casing sections are discussed from the aspects of the shear wave velocity and thickness of soft interlayer.The result shows that while shear wave velocity of soft interlayer decreases or its thickness tends to the critical value hcr,the bending moment and shear force of casing string at interfaces of soft interlayer will increase accordingly.Therefore,influence of soft interlayer on seismic response of casing string should be fully taken into account in marine engineering.