Study on rock-breaking mechanism of the vertical wheel PDC bits

Abstract

To address the issues of slow drilling speed and poor operational stability of PDC bits in hard and heterogeneous formations, a VW-PDC bit with an integrated axle structure is proposed. A variable parameter experimental bit device was developed, and indoor rock drilling experiments with varying parameters were conducted. The performance of the VW-PDC bit and the C-PDC bit in drilling Jiang'an sandstone, Maokou limestone, and heterogeneous rocks were compared and analyzed, along with the influence of key structural parameters of the VW on bit performance. The study results indicate that the ROP and torque of the VW-PDC bit are highly sensitive to changes in the relative protrusion height. The VW PDC bit achieves an ROP comparable to the C-PDC bit but with a lower torque response and smaller three-directional acceleration. When drilling in soft rock (Jiang'an sandstone), the VW PDC bit's ROP is similar to that of the C-PDC bit, with the equivalent torque reduced by 1%–34.35% and the three-directional acceleration reduced by 15%–70%. In harder rock formations, while the VW structure slightly reduces the ROP, it significantly lowers the torque and stabilizes the torque response. When drilling rocks with interbedded layers, the VW-PDC bit exhibits excellent stability, with lower torque fluctuation and smaller three-directional acceleration. The VW cutting structure provides cushioning protection and auxiliary cutting for the PDC teeth, enhancing rock-breaking efficiency and overall bit stability. The research findings offer theoretical support and technical means for the design and application of VW-PDC bit in gravelly and interbedded heterogeneous rock formations.