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处于狭长井筒中的钻柱,其动力响应受到钻具组合、内外钻井液流动以及钻井参数等因素的影响,钻柱动力失稳导致的剧烈振动是井壁坍塌和钻具失效的重要原因.考虑到钻杆和钻铤在刚度和线密度上存在很大的差别,论文将钻柱简化为单阶梯输液管柱,钻井液沿着钻柱内部向下泵入并从环空返回地面.耦合考虑钻柱自重、随时间简谐变化的波动钻压、稳定器以及钻井液的水动力和阻尼力,建立了直井中钻柱横向振动的解析模型.利用有限单元法离散为四阶常微分方程后,采用Bolotin法得到临界频率方程确定系统的不稳定区范围,研究了钻压、钻杆长度、稳定器安装位置、钻井液的流速和密度等参数对系统稳定性影响的机理.研究表明:钻压的平均值和波动幅值都是钻柱失稳的驱动因素,而系统的稳定性对处于受拉状态的钻杆的长度变化不敏感.在论文所研究的参数范围内,降低钻井液流速和密度、下移稳定器的安装位置均有助于增强系统的稳定性.
The dynamic response of the drill string in the narrow wellbore is influenced by the combination of the drill string, the flow of the drilling fluid inside and outside, and the drilling parameters. The severe vibration caused by the dynamic buckling of the drill string is an important reason for the collapse of the borehole wall and the failure of the drilling tool. There is a big difference in stiffness and linear density between the drill pipe and the drill collar. The paper simplifies the drill string to a single ladder string, and the drilling fluid pumped down the drill string and returned to the ground from the annulus. The self-weight of the drill string, the fluctuating weight-on-bit, the stability and the hydrodynamic and damping forces of the drilling fluid with the change of the harmonic wave over time are established, and the analytical model of the drill string transverse vibration in a vertical well is established. , The Boltzmann method was used to obtain the critical frequency equation to determine the instability range of the system and the mechanism of the influence of the parameters such as weight on bit, length of the drill pipe, stabilizer installation position, flow rate and density of drilling fluid on system stability was studied. The average and fluctuating amplitude of pressure are the driving factors of the drill string instability, and the stability of the system is insensitive to the change of the length of the drill rod in the tension state.In the parameter range The reduced flow rate and density of the drilling fluid, the mounting position of the stabilizer down all contribute to enhanced stability of the system.