深水吸力桩结构强度设计及海上安装实践
Structural strength calculation and offshore installation practice of deep-water suction pile
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摘要: 吸力桩不仅可为深水油气建井提供足够的承载力,其作为水下结构物基础在水下生产系统中应用也愈发广泛。由于吸力桩结构跨度大、作业环境及安装工况恶劣,海上安装作业结构稳定性面临挑战。以应用于南海某气田、直径8 m、总高19.68 m的大型吸力桩为研究对象,构建1∶1有限元模型,基于南海某气田作业环境,对吸力桩海上施工时拖航、吊装和安装三个工况下的典型安装过程进行研究,通过载荷计算分析得到各工况条件下的最恶劣情况。算例分析表明:拖航工况最大应力出现在横向负加速度+垂直向正加速度+纵向负加速度组合风载情形下,且高应力集中在吸力桩与驳船的固定处;吊装工况考虑吸力桩上的滞留水进行空气中和水下提升分析,高应力均出现在吊点焊接处,为现场作业重点关注区域;安装工况对吸力桩安装就位和管汇安装过程中的倾斜情况进行核算,均满足标准要求。结合以上计算和海上安装实践表明,吸力桩整体海上施工过程安全可靠,安装精度较高。相关研究成果可为深水吸力桩优化设计及海上安装提供参考。Abstract: Suction pile can not only provide sufficient bearing capacity for deepwater oil and gas well construction, but also be used more and more widely in subsea production systems as the foundation of subsea structure. The stability of suction pile structure in offshore installation faces challenges due to its large span and harsh working environment and installation conditions. Taking a large suction pile with a diameter of 8 m and a total height of 19.68 m applied to a gas field in the South China Sea as the research object, a 1∶1 finite element model was constructed. Based on the operating environment of the gas field in the South China Sea, the typical installation process of suction pile under transporting, lifting and installation during offshore construction is studied, and the worst conditions under each working condition are obtained through load calculation and analysis. The results show that the maximum stress under the transportation condition is negative transverse acceleration+vertical acceleration+Y negative wind load, and the high stress is concentrated at the fixed place between the suction pile and barge. In the lifting condition, the trapped water on the suction pile is considered for air and underwater lifting analysis. The high stress occurs at the welding point of the lifting point, which is the focus area of the field operation. The calculation of suction pile installation and inclination of manifold installation under the installation condition meets the standard requirements. Based on the above calculation, combined with the offshore installation practice, the whole offshore construction process of suction pile is safe and reliable, and the final installation precision is very high. The relevant research results can provide reference for the optimal design and offshore installation of deep-water suction piles.
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