Rock-breaking experiments and simulations of shaped cutters in hard rock formations

To address the challenges of rapid bit failure and high drilling costs associated with hard limestone in Sichuan Basin of China, we conducted rock-breaking experiments and simulations of shaped (cylindrical, ridge, and chopper) cutters. Rock mechanics, drillability, and acoustic emission indentation tests revealed the drilling resistance characteristics of the limestone: average uniaxial compressive strength of 202.472 MPa, tensile strength of 7.092 MPa, and drillability of 7.866. We evaluated the performance differences between the shaped cutters before introducing an efficient and innovative finite-discrete-infinite element method (FDIEM) to establish an interaction model between the shaped cutters and limestone. The simulation results indicated the following: (1) The shaped cutters demonstrated superior rock-breaking performance compared to the traditional cylindrical cutter. (2) Compared with the cylindrical cutter, the ridge cutter yielded the lowest peak indentation force and mechanical specific energy, with reductions of 8.71 % and 33.83 %, respectively. This confirmed that the ridge cutter had the optimal tooth profile for the target formation. Its rock-breaking mechanism relied on the convex edges to induce localized high stress in the rock, which enabled efficient rock fragmentation via a plowing mode while mitigating frictional resistance from cuttings. (3) The novel chopper cutter with its secondary step surface exerted a buffering effect on the cuttings, thereby achieving high cutting stability. This study provides theoretical and technical support for the design of personalized drill bits and the acceleration of the rate of penetration (ROP) in deep hard rock formations.