Optimizing the Cutting Efficiency of Shaped Polycrystalline Diamond Compact Cutters by Adjusting the Cutter Orientation

Summary While analyzing the polycrystalline diamond compact (PDC) bit kinematics and the dull bit photos, an interesting observation was noted: there was a misalignment between the pointed edge of shaped PDC cutters and the wear flat of these cutters. This misalignment meant that shaped cutters did not cut the rock with the desired pointed edge while operating under downhole conditions, thereby failing to fulfill their design purpose. To investigate the effect of this misalignment on the rock-breaking efficiency of shaped cutters, the numerical calculations were first used to predict the effective contact area between the cutter and the rock, which proved that there was indeed a misalignment between the normal line of the bit profile and the calculated effective contact area, especially for the cutters located at the nose and shoulder of the bit profile. That is, the current placement specification for PDC cutters in the drill-bit manufacturing process, aligning the pointed edge of shaped cutters with the normal line of the profile of the corresponding cutter pocket, is not appropriate and shall be further optimized. Hence, three types of laboratory tests were designed: single-cutter cutting test, offset cutting test, and offset-rotation cutting test. The results showed that the offset cutting mode was more consistent with actual downhole cutting conditions of PDC bits, where the cutters on the rear blade just contacted part of the grooves created by the cutters on the front blade. The offset cutting reduced the rock-breaking efficiency, and this negative impact of offset cutting was more severe on the shaped cutters. To address this issue, this work proposed to rotate the shaped cutters by 15° from the normal line of the bit profile. The test results showed that adjusting the tip orientation can effectively improve the rock-breaking efficiency of both shaped PDC cutters and their bits. This work provides new insights into the study of the rock-breaking efficiency of shaped cutters, which can guide the optimization of bit manufacturing specifications and the development of new cutter shapes.