深水钻井隔水管-钻柱耦合系统的双重非线性动力学行为研究

The exploitation of oil and gas resources in deep sea faces complex ocean climate and environment; hence, the requirements for the reliability of equipment and the safety of operation are of high standard. During the deep sea drilling, the riser, which swings along with the ocean environmental loads, is connected at the well head with one of the cluster wellbores whose upsides is straight and the downsides is curved, to form a complete exterior pipe whose geometric nonlinearity is high. Within such an exterior pipe, a drill string extends from the platform to the downhole. During the rotation of the drill string, both its vibrations in different directions and its whirl with different intensity occur, which triggers multi-point impacts and frictions between the drill string and its exterior pipe. This is understood as another sort of nonlinearity, namely, contact nonlinearity. However, the current investigation on the dynamics of a deep sea drilling tubular system is rare. This project is intended to develop a complete dynamic model for the riser-drill string coupling system with double-nonlinearity. Meanwhile, the description methods of nonlinear dynamics, such as bifurcation, chaos, and multistability, will be introduced to reveal the distribution characteristics of the system’s dynamic responses, and display the evolution paths of the dynamic behaviors of the system's dangerous positions. Moreover, based on multi-objective optimization and reliability analysis, an integrated design approach will be developed. By applying such an approach, the unstable motions of the drilling tubular system are expected to be avoided, hence a secured and optimized configuration for the deep sea drilling tubular system can be obtained, which is expected to be benefit for supporting the overall exploitation of the oil and gas resources in deep sea.

深水油气资源的开发，面临着复杂的海洋腹地气候与环境，对装备可靠性和作业安全性要求极高。在进行深水钻井作业时，随海流弯曲摆动的隔水管与上直下斜的丛式井筒在井口处连接，形成具有几何非线性的外部管柱。在其内部，从平台延伸到井底的钻柱在自转的同时伴随着不同方向的振动和不同强度的涡动，使得钻柱在不同深度处与隔水管或井筒发生多点碰撞和摩擦，呈现接触非线性。然而目前尚缺乏关于双重非线性因素耦合作用下管柱系统动力学行为特征的相关研究。本课题针对深水钻井隔水管-钻柱耦合系统的双重非线性特性进行整体的动力学建模与求解，并引入非线性动力学的分岔、混沌和多稳态等表征方式，完善对于非线性管柱系统动力学行为特性的认识。并在此基础上，构造基于多目标优化和可靠性分析的一体化设计方法，通过系统优化设计帮助管柱系统规避非稳定运动状态，实现深水钻井管柱系统的安全优化配置，为深水油气资源的全面开发提供技术支撑。

随着我国陆地油气资源量的减少和开采难度的增加，以及近海海域的油气开发逐步趋于饱和，对深水油气资源的开发已经成为我国石油工业新的发展方向。隔水管作为海洋油气开发过程中隔绝海水，运送钻柱和钻井液的通道，是深水钻井作业的重要装备。因此，准确地掌握隔水管系统的动力学行为特征是确保海洋钻井作业安全的关键所在。本项目以隔水管-钻井液-钻柱耦合系统为研究对象，通过理论分析、数值模拟、有限元仿真相结合的方式，围绕其非线性动力学行为规律及其可靠性优化开展研究。.具体而言，以海洋环境载荷作用下的深水钻井管柱耦合系统为建模对象，采用Hamilton原理与泛函变分相结合的方法建立动力学模型，并通过Hermite三次插值法将其离散为有限元模型，进而运用Newmark积分法和模态分析法讨论了隔水管壁厚、顶部张力、浮力系数、海流流速和海浪波高等参数对隔水管动力学行为的影响规律。此外，为了分析隔水管与钻柱之间的相互作用，提出了全新的漂移元模型来处理双移动管中管系统的碰撞问题，并通过与实验结果的对比，验证了该模型的正确性。.通过本项目研究发现，隔水管与钻柱的相互作用对海洋钻井管柱系统的整体偏移有明显的抑制作用；而钻井液对隔水管与钻柱之间的随机碰撞有缓冲作用，从而会降低管柱间碰撞对隔水管横向偏移的抑制作用。井身结构对隔水管动态响应也存在显著影响，这一影响是通过限制钻柱运动传导给隔水管的。井斜角越大，其井身结构对钻柱运动的约束作用越大，进而导致钻柱与隔水管之间的碰撞作用降低，最终导致隔水管的横向偏移量增大。此外，通过研究还发现隔水管的横向偏移程度会随着钻井平台的横向漂移量的增大而增大，而且钻井平台横向漂移量不同，隔水管的最大偏移位置也将不同。最后，通过与单目标优化设计方案的比较发现，多目标优化设计的整体优化程度更好，但为了确保深水钻井管柱系统即使在设计参数波动情况下仍然能满足最低的可靠度要求，应该在多目标优化设计方法中进一步引入可靠度优化算法。