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将弯曲井眼中的底部钻具组合作为空间梁处理 ,采用两个力学过程模拟指重表所示的指示钻压。利用“施加”与“放松”约束的方法求解钻柱与井壁间的接触摩擦非线性问题 ,并考虑了钻柱与井壁之间摩擦力的影响。在此基础上 ,建立了对弯曲井眼中的钻柱进行井底实际钻压分析的基本方程及相应的迭代求解格式。通过数值算例和工程算例得出结论 :(1 )由于钻柱与井壁之间存在摩擦 ,井底实际钻压比指示钻压小 ,在工作钻压较大时实际钻压比指示钻压小 1 5%～4 0 % ;(2 )井眼曲率对井底实际钻压的影响较小 ,而钻柱与井壁之间的摩擦系数对实际钻压影响较大 ,因此改善钻井液性能 ,降低摩擦系数十分重要 ;(3 )随着井深的增加 ,井底实际钻压与指示钻压的差值增大 ;若井眼曲率增大 ,实际钻压减小 ,指示钻压越大 ,其减小趋势越大 ;随着摩擦系数增大 ,实际钻压减小的趋势增大。
The bottom hole assembly in a curved well is treated as a space beam and two mechanical processes are used to simulate the indicated weight on the weight table. The non-linearity of contact friction between drill string and shaft lining is solved by means of “application” and “relaxation” constraints, and the influence of friction between drill string and shaft lining is considered. On this basis, the basic equation of the actual bottom hole WOB analysis for the drill string in a curved well and the corresponding iterative solution format are established. Through numerical examples and engineering examples, the conclusions are drawn as follows: (1) Due to the friction between the drill string and the borehole wall, the actual bit weight at the bottom of the well is smaller than the indicated bit weight. When the work-boring pressure is larger, (1) The pressure of borehole is less than 15% ~ 40%; (2) The influence of wellbore curvature on the actual bottom hole WOB is small, while the friction coefficient between drill string and wellbore has a great influence on the actual WOB. Therefore, (3) With the increase of well depth, the difference between the actual WOB and the weight on bit (WOB) increases. If the wellbore curvature increases, the actual WOB decreases and the greater the WOB, The trend of decreasing is bigger. As the friction coefficient increases, the actual reduction of bit weight tends to increase.