Rock-Breaking Mechanism and Performance of Arch-Ridged Cutters Used for PDC Bits

Summary As well depths continue to increase, the drilling conditions become more complex and challenging, causing the axe-shaped and tri-ridged cutters, usually used for their good impact resistance, to face premature impact failure. Inspired by dome- and ridge-shaped cutters, the arch-ridged cutters were developed in this work to enhance the cutter’s impact resistance without sacrificing the penetration rate. Arch-ridged structure incorporated the arch feature to improve the cutter’s impact resistance while retaining the ridge point feature to optimize the rock-breaking efficiency. To verify the rationality of this new cutter shape, discrete element modeling, laboratory single-cutter rock-cutting testing, progressive drop testing, wet vertical turret lathe (VTL) testing, and a field trial were conducted. The results showed the arch-ridged structure changed the rock-breaking mechanism of polycrystalline diamond compact (PDC) cutters based on real-time observations of its granite-cutting process. The arch feature enhanced the compression and crushing function of the cutter, while the ridge point feature led to the formation of three separate crushing zones, causing the sequential detachment of rock chippings from the ridge tip and the ridge slopes. When the depth of cut (DOC) exceeded 3 mm, the rock-breaking efficiency of arch-ridged cutter became comparable with that of axe-shaped and tri-ridged cutters, indicating that the arch-ridged cutter could obtain a satisfactory penetration rate under sufficient weight on bit. The biggest advantage of the arch-ridged structure was improving the impact resistance by more than 51% compared to axe-shaped and tri-ridged cutters. The bit deployed with arch-ridged cutters was trialed to drill a conglomerate formation at the Shengli Oil Field in China. The bit obtained the longest footage compared with adjacent wells, and the dull arch-ridged cutters had much less impact damage than the tri-ridged cutters. In short, the application scenario of the arch-ridged cutters is harsh formations that cause severe impact damage on PDC cutters, where the arch-ridged cutters can extend the bit footage with a moderate penetration rate.