Effect of Polishing on Cutting Efficiency and Mechanical Properties of PDC Cutters

Abstract

Summary Polycrystalline diamond compact (PDC) bits equipped with polished cutters have shown improvements in drilling performance compared to the bits using nonpolished cutters. Despite the positive feedback from numerous global field runs, the merits of polished cutters are still not fully studied and not taken seriously, for example, by the bit manufacturers and drilling engineers in China. In this work, the effect of polishing on the rock-cutting efficiency and mechanical properties of PDC cutters was comprehensively analyzed through laboratory tests and field trials. The underlying mechanism was also investigated through theoretical modeling and experimental results. A rock-cutting force model of a single PDC cutter was developed to elucidate the effect of polishing on the rock-cutter interaction considering the friction between the cutter surface and rock cuttings. The results revealed that the polished cutter has better rock-cutting efficiency because the polishing reduces the friction on the cutter surface. This reduction in friction facilitates the evacuation of rock cuttings from the crushing zone and plastic flow zone, leading to lower mechanical specific energy (MSE) compared to the nonpolished diamond surface. Moreover, the polished cutters exhibit improved thermal stability and better impact fatigue resistance while maintaining comparable wear and impact resistance to nonpolished cutters. To further validate the findings, two field trials were conducted in Sinopec Shengli Oilfield. The first field trial using four PDC bits with polished cutters and one bit with nonpolished cutters found that the bits with polished cutters obtained a higher rate of penetration (ROP) in drilling hard and plastic mudstone, which agreed well with the theoretical and experimental results. In the second field trial, it was noted that the polished cutters presented comparable mechanical properties to nonpolished cutters, which was also consistent with experimental results. However, the advantages of polished cutters in thermal stability and impact fatigue resistance were not distinguished in the field trials. This work elucidated the beneficial effect of polishing in enhancing the drilling efficiency of PDC cutters and, more meaningfully, without sacrificing the mechanical properties of PDC cutters, which provided solid evidence to convince bit manufacturers and drilling engineers for the broader adoption of polished cutters.