Abstract: Flexible drill rod with hinges is widely used in the drilling technology of ultra-short radius horizontal wells. The flexible drill rod is different from the conventional drill rod in that its deformation process is not only accompanied by the mutual transition between the mechanism and the structure, but also has random contact with the outer pipe. Considering the structural characteristics of the flexible drill rod with hinges, flexible drill rod and outer pipe are treated as spatial beam elements after processing by the finite element method, and the hinges are discretized into universal joint connection elements. The contact relationship between the flexible drill rod and the outer pipe is described using the contact gap element; a contact nonlinear finite element simulation model of flexible drill rod with hinges is established and further solved by introducing dynamic relaxation method. A plane model for the contact between the articulated beam and the outer beam is established to verify the feasibility of the finite element model and dynamic relaxation method. According to the superposition principle and deformation coordination conditions, the analytical expressions of deflection, contact force and other parameters are derived, and the numerical solution is compared with the theoretical solution, with the maximum error of only 0.14%. Simulation analysis is performed for the flexible drill rods with hinges that have six hinge rotation limits in the building up section. The results show that the contact force between the flexible drill rod and the outer pipe is intermittent and discontinuous and randomly distributed along the axis. The larger the hinge rotation limit is, the less change in torque is transferred to the bottom end of the flexible drill rod, and the axial force transferred to the bottom end of the flexible drill rod gradually decreases. When the hinge rotation limit is greater than 5°, the axial force loss rate is greater than 59.5%.

Key words: flexible drill rod, hinge, beam element, contact nonlinearity, dynamic relaxation method

摘要： 含铰柔性钻杆广泛应用于超短半径水平井钻井技术中。柔性钻杆不同于常规的钻杆，其在变形过程中不仅伴随有机构与结构之间的相互过渡，同时柔性钻杆还与外管产生随机接触。考虑含铰柔性钻杆的结构特点，采用有限单元法将柔性钻杆和外管均处理为空间梁单元，将铰离散为万向节连接单元，柔性钻杆与外管之间的接触关系采用接触间隙元进行描述，建立含铰柔性钻杆接触非线性有限元仿真模型，引入动力松弛法对其进行求解。为验证有限元模型及动力松弛法的可行性，建立了铰接梁与外梁接触平面模型，根据叠加原理和变形协调条件推导了挠度、接触力等参量的解析表达，将数值解与理论解进行比较，最大误差仅为0.14%。对造斜段6种铰接转动极限的含铰柔性钻杆进行仿真分析。结果表明，柔性钻杆与外管之间接触力是间断不连续的，且沿轴线随机分布，铰接转动极限越大，传递到柔性钻杆底端的扭矩变化不大，传递到柔性钻杆底端的轴力逐渐减小，铰接转动极限大于5°时，轴力损失率大于59.5%。

关键词: 柔性钻杆, 铰, 梁单元, 接触非线性, 动力松弛法