指向式旋转导向系统内外环转速对PDC钻头破岩效率的影响

为了提高指向式旋转导向钻井工具的破岩效率，在钻头运动学研究的基础上，利用Matlab软件建立了数字化PDC钻头模型和数字化岩石模型，结合岩石模型的离散化处理，模拟了旋转导向钻进条件下，PDC钻头与岩石的相互作用过程，并给出了破岩效率的定量计算方法；分析了指向式旋转导向系统内外偏心环转速对PDC钻头破岩效率的影响，得到了不同时间步长下的破岩规律。研究结果表明，抗剪强度为11 MPa、内摩擦角为22°、摩擦系数为0.2的岩石，其最佳破岩转速比在1.0左右，且指向式旋转导向系统在钻进过程中均存在稳态切削，其破岩效率与内外偏心环的转速比密切相关，随着内外偏心环转速比增大，破岩效率也相应增大，但最终趋于稳定。研究结果对提高指向式旋转导向系统的钻井效率具有一定的理论指导作用。 

Influence of the Rotary Speeds of the Internal and External Rings of Pointed Rotary Steering System on the Rock-Breaking Efficiency of PDC Bit

The goal was to improve the rock-breaking efficiency of the pointed rotary steering drilling system. To do so, a new process was developed, based on the research of bit kinematics, the digital PDC bit model and the digital rock model. The team used Matlab software, which, combined with the discretization processing of rock model, was able to simulate the interaction between PDC bit and rock under the condition of rotary steering drilling, and further obtain the quantitative calculation method of rock-breaking efficiency. The influence of the rotary speeds of the internal and external rings of pointed rotary steering system on rock-breaking efficiency of PDC bit was analyzed, and the rock-breaking law at different time steps was obtained. The results showed that for the rock with a shear strength of 11 MPa, an internal friction angle of 22o and a friction coefficient of 0.2, it had an optimal rock-breaking speed ratio of about 1.0, and the pointed rotary steering system presented a steady state cutting during the drilling process. Its rock-breaking efficiency was closely related to the speed ratio of the inner and outer eccentric rings. As the speed ratio increased, the rock-breaking efficiency also increased, but it eventually stabilized. The research results demonstrated a possible theoretical guidance for improving the drilling efficiency of pointed rotary steering system.