Experimental research on efficiency and vibration of polycrystalline diamond compact bit in heterogeneous rock

To explore the rock-breaking efficiency and vibration characteristics of polycrystalline diamond compact bit in heterogeneous rock, this paper analyzes the typical vibration characteristics and failure modes of polycrystalline diamond compact bit. Then, the transverse combination of rocks was innovatively used to simulate a situation of soft-hard interbedded formation, forming three kinds of transversely combined heterogeneous rock samples with different degrees of heterogeneity. We conducted a series of laboratory rock-breaking experiments and the experimental results indicate that rock heterogeneity greatly impacted vibration acceleration, lateral bending moment, rate of penetration, and drilling trend. With the increase in weight on bit and rotation speed, the rate of penetration gradually increases. However, the tangential, axial, and radial vibration acceleration amplitude of the bit all increase simultaneously, which implies that the vibration impact generated by rock-bit interaction increased. The difference in the cutting depth of the drill bit in the heterogeneous formation causes low efficiency. The stronger the heterogeneity, the lower the rate of penetration. Rock heterogeneity, especially the rock properties of the combined rock samples, significantly impact acceleration and lateral bending moment. As rock heterogeneity increased, the bit acceleration increased significantly, intensifying the bit vibration; the lateral bending moment increased slightly, but its fluctuation intensified. The strength difference of heterogeneous rock causes eccentricity, the harder rock exerts greater force on the bit, causing the bit to deviate from the original trajectory. The greater the difference, the greater the eccentricity, consequently, the more the bit shifts to the softer side. Adjusting rotation speed and depth of cut control may be feasible solutions to solve the problem of low drilling speed and high vibration in heterogeneous formation. It is hoped that the findings in this paper will be helpful to explore a reasonable way to reduce vibration while maintaining high efficiency.