Numerical simulation and experimental study on the interaction between a convex ring PDC bit and rock

Abstract

To address the problems of low rock-breaking efficiency and high energy consumption of polycrystalline diamond compact (PDC) bits in hard formations of deep well sections, a convex ring PDC bit is proposed that alters the stress distribution law of the smooth bottom hole of a conventional PDC bit and forms a double-order stress state of the bottom-hole rock. The interaction law between the convex ring PDC bit and rock is explored by combining numerical simulation and experiment. The numerical simulation of conventional PDC bit and convex ring PDC bits is conducted using the discrete element method. The simulation results show that the stress concentration occurs at the convex ring of the new drill bit, resulting in multiple main cracks and facilitating volume crushing. The surrounding compressive stress ring formed by the new drill bit exhibits obvious pressure differences, which can effectively induce the penetration of cracks. The location and size of the convex hull structure have an important influence on the rock's damage law. The experimental results show that the potholes in the bottom hole morphology of the new bit are significantly larger than those of the conventional bit, and the formed cuttings are a factor of 1–2.5 larger than those of the conventional bit. The new PDC bit has a critical WOB, when the WOB exceeds the critical value, the mechanical specific energy of the new bit is lower than that of the conventional bit, and the ROP is higher than that of the conventional bit, it has better rock-breaking efficiency. These research results should provide a theoretical basis for the application and promotion of the new convex ring PDC bit.