深水钻井隔水管悬挂撤离动力学特性与涡激振动机理研究

Drilling risers are key equipment in deepwater drilling and they need to be hung-off with the drilling platform when the typhoon comes. Deformation and vortex-induced vibration occur under the effect of the ocean environment and movement of the drilling platform. The fracture accident may occur while the evacuation parameters are not appropriate. At present, the fact that the dynamic characteristics and mechanism of vortex-induced vibration for the hang-off conditions of deepwater drilling riser under the effect of different ocean environments and drilling platform courses and speeds is limited. It is difficult to insure the safety leave of the drilling riser and platform. The project intends to develop a facility for mechanical behavior of deepwater drilling riser under hang-off conditions based on similarity principle, establish a new dynamic and vortex-induce vibration model for deepwater drilling riser under the hang-off conditions based on experimental results considering ocean environment, drilling platform course and speed, hang-off type, riser system configuration and weight of the lower marine riser package, etc. And study the dynamic characteristics and mechanism of vortex-induced vibration such as deformation, vibration mode and response frequency for deepwater drilling riser under the hang-off conditions through the experimental and theoretical simulation methods. It will solve scientific issues of unclear understanding of the dynamic characteristics and mechanism of vortex-induced vibration for the hang-off conditions of deepwater drilling riser under the effect of different factors such as ocean environments and drilling platform course and speed. Meanwhile, it can provide theoretical guidance for determining evacuation parameters such as riser hang-off length, hang-off type and drilling platform course and speed. What’s more, it has important academic value for understanding the mechanical behavior of the deepwater drilling riser under hang-off conditions, and would expand tubing string mechanics theory of oil and gas well.

隔水管是深水钻井的关键设备，台风来临时需随平台悬挂撤离，在海洋环境与平台运动作用下产生变形与涡激振动，若撤离参数选择不当会导致安全事故发生。目前，针对海洋环境与平台运动等多因素耦合作用下，隔水管悬挂撤离动力学特性与涡激振动机理认识有限，难以确保隔水管安全撤离。本项目拟基于相似原理建立深水钻井隔水管悬挂撤离力学行为实验装置并开展实验；以实验数据为基础，耦合海洋环境、平台航速与航向、悬挂模式、系统配置和底部总成重量等因素，建立隔水管悬挂撤离动力学与涡激振动分析新模型，采用实验与理论相结合的方式研究隔水管悬挂撤离时变形、振动模态与频率等力学特性，拟解决当前对复杂海况与平台运动耦合作用下隔水管悬挂撤离动力学特性与涡激振动机理认识不清的科学问题，也为隔水管悬挂长度、模式与平台航向航速等参数的确定提供理论指导。研究成果对认识隔水管悬挂撤离力学行为具有重要理论价值，同时也是油气井管柱力学理论的重要发展。

隔水管悬挂撤离时，除受到海洋环境载荷作用外，平台运动也会引起海水对隔水管的载荷作用，极易导致隔水管断裂失效。项目开展以来，基于相似理论设计并研制悬挂撤离模式下隔水管力学行为实验装置，开展了不同海流流速、平台航速与航向、悬挂模式、悬挂长度、隔水管系统配置、LMRP重量等因素耦合作用下隔水管悬挂撤离力学行为实验研究；耦合平台航速与航向、海洋环境载荷、悬挂模式与长度、LMRP重量等因素，建立了悬挂撤离状态下隔水管动力学以及涡激振动模拟模型，并通过实验验证了模型，分析了不同因素耦合作用下隔水管动力及涡激振动特性，评价分析了不同工况下深水钻井隔水管悬挂撤离动力学特性，校核其不同工况下的强度。研究结果表明：悬挂撤离隔水管时，软悬挂模式下，极大应力出现在水面附近；硬悬挂模式下，出现在隔水管与平台连接处。平台和海流的速度直接影响隔水管的变形和弯矩，保持平台撤离方向与撤离速度尽量接近海流方向与速度有利于保障悬挂隔水管的安全。较重的LMRP可以减少隔水管变形和弯矩，但会显著增加隔水管轴向张力以及平台承重，对于悬挂较重LMRP的撤离隔水管可以承受更大的环境负荷以更高的速度撤离。在保证隔水管上部接头安全的情况下，适当回收隔水管减小悬挂长度可以减小整个隔水管的变形；较短的悬挂长度有利于减少隔水管的整体变形，但却反而会导致顶部连接处弯矩增大。软悬挂模式下采用旋转刚度适当较大的的挠性接头则有利于减小隔水管挠性接头以下整体位移与弯矩。与硬悬挂模式相比，软悬挂模式下隔水管整体弯矩与应力都更小，但是由于顶端转角较大容易碰撞月池，软悬挂模式下隔水管所能承受海流作用能力并不能显著优于硬悬挂。因此，平台撤离时不能盲目采用软悬挂或硬悬挂模式，应当结合实际情况选择合适的悬挂模式。研究结果将为优选不同工况下隔水管悬挂撤离模式、悬挂长度、平台航速与航向等参数提供重要的理论依据。