深水钻井隔水管脱开模式下纵向动态行为研究

Research on the Dynamic Behavior of Riser in Deepwater Drilling under the Condition of Disconnection Mode

钻井隔水管在一些特殊情况下会与水下井口紧急脱开,其纵向固有频率很有可能落入波浪的能量窗口而发生纵向共振,造成隔水管损坏,甚至有可能对平台造成损伤。将隔水管视为均质等截面弹性细直杆,建立了隔水管纵向振动波动方程。把隔水管的纵向振动视为自由振动,根据边界条件,利用数值方法,求出了隔水管纵向自由振动的固有频率。考虑动态放大系数计算了隔水管的动态载荷。计算结果表明,隔水管的自身重量影响其纵向振动的固有频率和动态载荷,并根据此提出了避免隔水管与波浪发生共振,减少其动态载荷的方法。

In some specific cases,the drilling riser would disconnect from subsea wellhead.Its axial frequencies may fall in the energy window of wave;this will cause resonance,which may damage riser and platform.Taking the riser as a long homogeneous slender rod with same cross section,a longitudinal vibration equation was derived.Regarding the longitudinal vibration of riser as a free vibration,an inherent frequency of riser vibrated in free way longitudinally was found using boundary condition by numerical method.A dynamic load of riser was calculated considering dynamic magnifying factor.Results show that gravity of riser has an effect on the inherent frequency and dynamic load of riser.A method to reduce dynamic load of riser and to avoid resonance between riser and waves was given.