偏轴钟摆钻具组合力学特性分析

运用纵横弯曲连续梁理论和达朗伯原理 ,建立了偏轴钟摆钻具组合动力学分析模型。该模型能够用于求解钻头处的侧向力和转角以及偏轴接头处的侧向力 ,以评价钻具组合的防斜 (纠斜 )能力和偏轴接头附近的偏磨程度。计算结果表明 ,适当降低钻压或提高转速 ,有利于纠斜 ;增加偏轴接头偏心距或将偏轴接头位置上移 ,有利于纠斜 ,但不利于控制钻铤 (或接头 )偏磨 ;扶正器位置上移基本上不利于纠斜 ,也不利于控制钻铤 (或接头 )偏磨 ;偏轴接头处存在较大的接触力时 ,适当调整钻井参数或钻具结构能够避免或减轻钻铤偏磨

Mechanics analysis of the offset-axes pendulum drill assembly

A mechanical model for the offset-axes pendulum drill assembly (OAPDA) was established according to the continuous beam theory and the D.Alembert principle. The lateral force and the tilt angle on bit can be calculated with this model and used to evaluate the deviation control capability of OAPDA. The lateral force on offset-axes sub can be calculated and used to evaluate the eccentrically wearing degree near the offset-axes sub. The calculated results show that decrease of weight on bit (WOB) or increase of the rotary speed is propitious to deviation control, and increasing the offset distance of offset-axes sub or moving up the offset-axes sub is also propitious to deviation control, but it is unable to control the eccentrically wearing degree. Moving up the stabilizer goes against to control the deviation and eccentrically wearing degree. When the contract force on offset-axes sub is quite large, the eccentrically wearing degree of drill collar can be reduced by adjusting the assembly or drilling parameters.