钻柱轴向振动固有频率的计算和测量

钻柱振动的固有频率是钻柱在给定钻具组合（ＢＨＡ）条件下钻柱振动的固有特性，在钻进过程中钻头与地层相互作用对钻柱产生激励振动，如果某一激励频率与钻柱自身的固有频率相近时，钻柱将产生共振现象．共振对钻柱是有害的，它可以引起钻柱局部的应力集中，导致钻柱断裂，发生井筒事故．共振与钻井参数有直接关系，如钻压、转盘转数、泥浆性能等，因此，通过调整钻井参数可以避免钻柱的共振现象，达到优化钻井的目的．给出了钻柱轴向振动的固有频率和振动传输公式．现场测量及计算表明，不是所有的固有频率点都会引起钻柱的强烈振动，它取决于振动传输比，现场试验数据验证了计算公式．通过固有频率的计算，分析了减震器对固有频率的影响以及固有频率随井深增加的变化趋势．

Calculation and Measurement of the Natural Frequency of Axial Drillingstring Vibration

The natural frequency of drillingstring vibration is its inherent character under certain bottom hole assembly(BHA). In drilling, the interaction of bit and downhole rock will excite the vibration of drillingstring. When the frequency of exciting vibration approaches the natural frequency of the drillingstring, resonance will occur. Intense resonance will lead to the local stress concentration of drillingstring, even its fracture and wellbore troubles. The exciting frequency is directly related to drilling parameters such as weight on bit, the revolution rate of rotary, mud property, and so on.So thd resonance can be avoided by adjusting the drilling parameters. The formulas for calculating natural frequency and vibration transmission ratio are given. The calculated results and field measured data all show that the intense vibration of drillingstring does not take place at all natural frequency points, and it depends on vibration transmission ratio. The formulas are verified by the data measured in Gu 108 well of Huabei Oil Field. By calculating natural frequency, the influence of vibration absorbor on it and the varing tendency of it with the increase of well depth are analyzed.