基于应力刚化效应的直井钻柱横向振动分析

Analysis of transverse vibration of drill string in vertical well based on stress stiffening effect

钻柱建模对象的选取和钻柱轴向力对直井钻柱的横向振动特性分析有很大的影响。本文根据求解几何非线性问题的有限变形理论,考虑钻柱自重和钻压的反向作用力产生的应力刚化效应,建立钻柱动力学方程。运用有限元法分别对整体钻柱和底部钻具进行无轴向力的横向振动分析,对比后选取整体钻柱作为后续研究对象,然后分别进行以轴向力作为预应力的模态分析、谐响应分析和瞬态动力学分析。结果表明,与底部钻具相比,无轴向力作用下整体钻柱的固有频率很低且钻铤处振动不明显;考虑轴向力时,自重产生的拉力会显著提高钻柱的固有频率,钻压产生的反向力会降低钻柱的固有频率,中性点附近钻铤的横向振型变化较大,钻杆的横向振动从井底到井口逐渐减弱;钻压为50 kN、钻柱转速在0~90 r/min之间时,存在0.4~0.6 Hz(对应转速为24~36 r/min)的共振微弱区,同时钻压越大,共振微弱区的频率越低;钻柱与井壁发生碰撞后,轴向力使钻柱中性点处的振动能量增大但振幅降低。

Modeling objects and axial forces of the drill string have great impact on the analysis of transverse vibration characteristics of the drill string in vertical wells.With the stress stiffening effect caused by reverse forces of drill pressure and drill string weight considered,dynamic equations of the drill string were established based on finite deformation theory for geometric nonlinearity issues.Finite element method was used to analyze transverse vibrations of the whole drill string and the bottom drill without axial force.After comparison,the whole drill string was selected as the follow-up research object.Then modal analysis,harmonic response analysis and transient dynamic analysis with axial force as prestress were carried out respectively.The results show that,compared with the bottom drill,the inherent frequency of the whole drill string without axial force is much lower and the vibration of drill collar is less obvious.When the axial force is taken into account,the inherent frequency of the drill string is significantly increased by the tension due to drill string weight and decreased by the reverse force due to drill pressure;transverse vibration mode of the drill collar near the neutral point changes greatly,and transverse vibration of the drill string is gradually weakened from the well bottom to the well top.When drill pressure is 50 kN and drill speed is 0~90 r/min,there is a weak resonance region of 0.4~0.6 Hz(corresponding to the speed of 24~36 r/min),and the greater the drill pressure,the lower the frequency of the weak resonance zone.When the drill string collides with the borehole wall,the axial force increases the vibration energy at the neutral point of the drill string but decreases the vibration amplitude.