PDC钻头切削破岩机理及数值模拟研究
Exploring Mechanism and Numerical Simulation of Rock Breaking Process Using PDC Bit

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 (polycrystalline diamond compact) bits' geometry, rock materials and a downhole's working conditions, its cutting rock breaking mechanism has always been a puzzle. Using the single tooth cutting mechanism and introducing the specific energy ε of rock, we find the relationship among Weight On Bit (WOB) w, torque t and cutting depth d and establish the two-dimensional diagram (E-S) between cutting specific energy (E) and drilling strength (S). The concept model of rock fragmentation is elaborated by using the frictional component. The 3D non-linear dynamic model of dynamic rock breaking with a full-gauge PDC bit is established with the finite element method, which can be used to further analyze the response of rock-breaking processes of the PDC drill bit. The analysis results show that the rock damage and the stress cloud can directly reflect the wellbore formation following the peeling of the damaged rock and the stress distribution of the downhole during the drilling process. The displacement, acceleration and torque responses of the PDC drill bit in its drilling direction well coincide with the theoretical analysis and not only interpret the "footage step" in the drilling process but also evidence the conceptual model of the rock breaking process