Effects of the chamfer and materials on performance of PDC cutters

Polycrystalline diamond compact (PDC) cutters play a key role in the performance of PDC bits in the oil & gas drilling. The study of single cutter on the rock-breaking mechanism is very important for PDC bits to deal with challenging formations, especially when the wells become increasingly longer and complex. Both cutting efficiency and durability are always the focuses of attention for the researches on single PDC cutter. Of all the factors influencing the cutting efficiency, the chamfer is always ignored in theoretical and experimental studies. In this work, the rock-cutter interaction model was modified with considering the effect of the chamfer, which could be used to predict the cutting forces and cutting efficiency of PDC cutters while shearing the rocks. All cutters have been tested on a vertical turret lathe to verify the modified theoretical model. The accuracy of the theoretical prediction agreed well with the experimental results. It was found that the cutting efficiency could be greatly enhanced by reducing the chamfer size for the cylinder-shaped PDC cutters. Unfortunately, the small chamfer size made PDC cutters vulnerable to the premature failure. In order to improve the durability of small-chamfered PDC cutters while retaining their cutting efficiency, an optimized mix of diamond grains was developed and experimentally studied. The results illustrated that the cutter with optimized diamond mix exhibited much better wear resistance. On the other hand, the chamfer size has relatively weak effect on the wear resistance of PDC cutters. The increased chamfer size contributes to protect the cutter edge from chipping but will cause more cumulative friction heat and impair the cutter's durability. The findings in this work will provide a valuable guideline for the manufacturers of PDC bits.