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由于PDC钻头几何外形、岩石材料以及井底钻井工况的复杂性,PDC钻头切削破岩机理的研究一直都是难点问题。基于单齿切削机理,引入岩石比功ε,推导出钻井钻压W、扭矩t和切削厚度d之间的关系,建立切削比功E与钻井强度S的二维图;同时结合接触摩擦分量,分析并阐述了破岩过程的概念模型;通过有限元方法建立全尺寸PDC钻头动态破岩的非线性动力学三维仿真模型,开展PDC钻头切削破岩机理的研究,进一步分析PDC钻头破岩过程的响应规律。结果表明:岩石损伤与应力云图可直观反映钻井过程岩石损伤剥落形成井眼及井底应力分布状况;PDC钻头钻进方向的位移、加速度和扭矩响应规律与理论分析相一致,并揭示了PDC钻头钻进过程中的“进尺台阶”现象,亦佐证了破岩过程的概念模型。
Due to the complexity of PDC bit geometries, rock materials and bottomhole drilling conditions, the research on PDC bit cutting and rock breaking mechanism has always been a difficult issue. Based on the single tooth cutting mechanism, the specific power of rock ε is introduced to deduce the relationship between drilling weight W, torque t and cutting thickness d, and to establish a two-dimensional map of the cutting work E and the drilling strength S. Combined with the contact friction component, The conceptual model of rock breaking process is analyzed and elaborated. The nonlinear dynamic three-dimensional simulation model of full-size PDC bit dynamic rock breaking is established by finite element method. The PDC bit cutting rock breaking mechanism is studied, and the PDC bit breaking rock process is further analyzed Response rules. The results show that the rock damage and stress cloud can directly reflect the wellbore and bottom hole stress distribution during the drilling process. The displacement, acceleration and torque response of the PDC bit are in accordance with the theoretical analysis. The PDC bit During the drilling process, the “walk-in step” phenomenon also proved the conceptual model of the rock breaking process.