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.