INVESTIGATE ON THE MIXED-CUTTING OF SPECIALLY-SHAPED PDC CUTTERS IN GRANITE

Due to the serious problems of cutter abrasiveness and damage in drilling by PDC bits with conventional cutters in hard formation, various specially shaped cutters have been widely used in the bit design. To explore and to optimize the cutter arrangement of PDC bits with the same or mixed shaped cutters and to improve the rock breaking efficiency in granite formation, the rock cutting test using the same shaped PDC cutters and rock cutting simulation of mixed cutters with planar cutters and specially shaped cutters are conducted. The results show that: the optimal space of cutters is 10 mm for the planar cutter, 12 mm for the axe-shaped cutter, 3 mm for the conical cutter and, 11 mm for the tri-plane cutter respectively with a cutting depth of 1.0 mm. In terms of the mixed cutter arrangement, the optimal space of cutters is 6 mm for 'planar and axe-shaped cutters', 8 mm for 'planar and conical cutters' and, 9 mm for 'planar and tri-planar cutters' in turn. Among the different combinations, the combination consisting of tri-plane cutters has the smallest mechanical specific energy and largest rock breaking efficiency. In general, the results of this study play a significant role in the selection of cutter shape for a single or a hybrid PDC bit and optimization of cutter gaps.