铅垂井段钻柱的动力分岔研究

基于弹性大变形理论,考虑到轴力沿钻柱轴线的变化及其对钻柱弯曲变形的影响等因素,将受自重作用的铅垂井段钻柱在波动钻压激励下的振动转化为一个参数激励系统,用Galerkin方法首次得到了描述此系统的Mathieu方程,并通过将方程的解展成富里叶级数的方法,得到了该振动系统的动力分岔值曲线及其所包围的动力不稳定区。当钻井作业参数落在动力不稳定区时,钻柱将发生破坏性振动。根据钻柱的物理与几何性质及钻柱的工作状态,首次推导出了参数激励系统分岔参数的计算公式,并据此开发了相应的程序模块。该模块可以根据钻井现场的实际情况,提供合理的转速和钻压等作业参数,以避开动力不稳定区,改善钻柱的工作状态,延长其工作寿命。

DYNAMIC BIFURCATION OF THE DRILLSTRING IN VERTICAL SECTION

Based on the elastic theory of large deflection and by taking into account the variation of the axial force and its effects on bending deformation of the drillstring in vertical section,the vibration of the drillstring induced by fluctuating weight on bit is described by a parametrically excited system.A Mathieu equation describing the system is established by Galerkin Method.By extending the solution into a Fourier series,the curves of dynamic bifurcation values and the dynamically unstable regions surrounded by the curves are presented.When the well drilling parameters appears in the dynamically unstable zones,the destructive vibrations would take place.The bifurcation parameters of the system are formulated in terms of the physical and geometric character and the working state of the drillstring.A corresponding computer block for the calculation of these parameters is programmed.The block allows drilling engineers to optimize the drilling parameters including rotary speed,weight on bit etc.,to avoid the parameters from being in the dynamically unstable areas,so as to improve the operating state and to prolong the working life of the drillstring.