Comparison of Fracture Characteristics of Different PDC Cutters Penetrating Carbonate Rock

Carbonate rock is a very important reservoir rock in many parts of the world, but due to high temperature, high hardness, strong abrasiveness and other reasons, PDC (Polycrystalline Diamond Compact) bit is seriously worn and the efficiency of breaking rock is low. To solve this problem, a lot of research has been carried out on the cutting mechanism of PDC cutters, but less research has been done on the crushing mechanism of PDC cutters penetrating carbonate rock. Actually, effective penetration can increase the cutting depth and change failure mode of rock. Furthermore, the PDC cutter penetration process will also cause damage to the rock, which is conducive to improving the subsequent efficiency of cutting rock. Therefore, the study of PDC cutter penetrating rock characteristics can provide theoretical basis for drilling parameter optimization and PDC bit structure design. In this paper, the crushing mechanism of PDC cutters penetrating carbonate rock was studied. Based on the hydraulic servo experimental system and ST400 3D Profilometer, a series of experiments were carried out on conventional cutter, axe cutter and conical cutter penetrating carbonate rock at different back rake angles. The penetration force-penetration depth curve and surface topography of broken pits were analyzed. The results show that the failure mode of carbonate rock is affected by the back rake angle of cutter. Conical cutter has strong aggression when penetrating at a small back rake angle. The expansion of axe-shaped angle of the axe cutter exacerbates the failure of carbonate rock. Moreover, at the back rake angle of 10° and 20°, the maximum penetration depth and penetration efficiency of conical cutter were significantly greater than those of conventional cutter and axe cutter. At the back rake angle of 30° and 40°, the maximum penetration depth of axe cutter is greater than that of conventional cutter and conical cutter. The research results are expected to provide theoretical guidance for the optimized design of PDC cutter shape and back rake angle.