定向钻井PDC钻头三维钻速预测方法

综合考虑PDC钻头的切削作用、钻具组合的力学作用和地层岩石可钻性各向异性,根据钻头力平衡原理,建立一种新的PDC钻头三维钻速预测方法。在钻头瞬态力平衡计算中,不仅考虑钻具组合的力学作用,还考虑钻头冠部的侧向不平衡力和保径受力对PDC钻头切削作用的影响。结果表明:井眼轨迹的预测结果与实测结果有较高的吻合度,说明方法合理;根据具体的钻头结构参数和地层可钻性各向异性,通过数值计算可获得钻头的轴向和侧向钻速,不需要取得地层法向钻进效率;在钻头瞬态力平衡计算中,钻头侧向不平衡力过大将增大井眼轨迹控制的难度,对PDC钻头布齿参数的进行优化设计可以减小钻头的侧向不平衡力,进而减小钻头漂移角和工具面变化范围,增强井眼轨迹控制能力。

A novel prediction method of PDC bit 's ROP in directional drilling

In this study, a novel prediction method of PDC bit ''s ROP during directional drilling was established, in which the cutting action of the PDC bit, the mechanical action of BHA and the drillability anisotropy of rock formations were considered based on the instantaneous force balance principle. In the calculation of the total transient force on the PDC bit, the influence of the lateral unbalanced force on bit crown and the lateral force on bit gauge were accounted. The new method was verified using the experimental results of core drilling, in which the predicted well trajectory has a good agreement with the measured one. In using this method, the axial and lateral drilling rate of the PDC bit can be obtained by numerical calculation based on the parameter of the bit design and the drillability anisotropy of the rock formation, and no need to measure the normal formation drilling efficiency of the bit. In consideration of the transient force balance on the bit, the higher the lateral unbalanced force, the harder for well path control. The lateral unbalanced force on the PDC bit can be decreased by optimizing the PDC bit design, and the drift angle of the bit and the variation of the tool face azimuth can be also decreased.