Numerical Simulation of Rock-Breaking Mechanism of Multicutter of Polycrystalline Diamond Compact Bits under Coupling Effect of Dynamic and Static Loads during Rotary Percussive Drilling in Deep Hard Rock Formations

Summary When drilling in high-strength, abrasive rock formations, rotary percussion drilling technology has garnered widespread attention for its efficient rock-breaking capabilities. However, existing investigations into the compatibility of polycrystalline diamond compact (PDC) cutters with rugged rock formations are still insufficient. Accordingly, based on rock dynamics theory, a numerical model for rock cutting by single-, dual-, and triple-cutter combinations composed of conventional cutters and special-shaped cutters, under dynamic-static load coupling, was established. The influence of laws of cutter type, rake angle, and cutter spacing with reference to depth of penetration and rock fragmentation output was assessed; the variation laws of rock-breaking effects under combinations of different cutter types and numbers were analyzed, and the multicutter rock-breaking mechanism under percussion drilling conditions was revealed. Research outcomes indicate that the axe cutter outperforms the planar cutter remarkably in terms of rock-breaking efficiency—its average penetration depth reaches 6.81 mm, which is 49.48% higher than that of the planar cutter (3.44 mm), and the corresponding cutting area (216.87 mm2) is also 54.0% larger than that of the planar cutter (140.81 mm2); among different cutter shape combinations, compared with the single-cutter setup, the dual-cutter structure outperforms in rock-breaking efficiency, and the combined planar-axe cutter arrangement attains the optimal effect; concerning the rake angle adjustment of the multicutter system, the optimal rake angle range for the front cutter is 15–20°, and the rear cutter achieves the best secondary fragmentation effect when its rake angle is 10–15°; in terms of the spacing setting in the multicutter system, the lateral spacing exerts a minor influence on the penetration depth, but the cutting area increases significantly with the increase in lateral spacing (with a total increment of 50.83 mm2); the effect of longitudinal spacing on penetration depth is deemed insignificant, but due to the reduced overlap of cutting zones, the cutting area gradually decreases as the longitudinal spacing increases (from 211 mm2 to 179 mm2). The findings provide valuable guidance for optimizing cutter geometry, designing cutter arrangements on drill bits, and enhancing drilling efficiency in deep formations.