深井钻柱疲劳强度计算与分析

钻柱疲劳失效的机理分析表明,钻柱在振动和进动工况下,受到拉、压、弯、扭等组合交变应力作用,发生疲劳破坏是其失效的主要形式。通过钻柱受力分析,给出钻柱轴向应力、弯曲应力、扭转应力、径向和周向应力,以及附加剪应力的计算公式。根据疲劳强度理论,建立了钻柱在不对称循环应力状态下的疲劳强度条件。结合实际算例分析,找出钻柱危险点处疲劳安全系数随井深、转盘转速和钻压的变化规律,有助于钻井参数的调整。

Calculation and analysis of fatigue strength of drill string in deep well

The mechanism analysis of drill string fatigue failure indicates that the fatigue breakage is the main form of drill string failure under the combined action of tension, pressure, buckling and torsion in its vibration and precession operations. The force analysis of the drill string is carried out to obtain the calculation formulas of its axial stress, bending stress, torsion stress, radial stress, circumferential stress and additional shearing stress. The fatigue strength condition of the drill string is established under the condition of asymmetry circle stress according to the fatigue strength theory. The actual case study is used to find out the change rule of fatigue safety coefficient at the risk point of the drill string with well depth, the rotating speed of the rotary table and drilling pressure, which is conducive to the adjustment of drilling parameters.