The Rock Breaking Mechanism of the Compound Percussive-Rotary Drilling Method with a PDC Bit

To provide satisfactory solutions to the low rate of penetration (ROP) and pre-mature failure of the PDC bits caused by stick-slip vibration while drilling through hard formations, an innovative compound percussive-rotary drilling technique with a PDC bit was proposed in this paper and the rock-breaking mechanisms of the technique were reviewed. By using the torsion models for one-way axial percussions and compound percussion of PDC bits, patterns of movements of such PDC bits were analyzed. In addition, ABAQUS was used to simulate shearing forces on rocks during one-way axial percussion and compound percussion. Research results showed that PDC bits under one-way axial percussion may have significantly enhanced the cutting depths of the teeth. At the same time, PDC bits may experience torsional vibration during the process, and compound percussion could significantly enhance shearing performances of PDC bits on formation rocks by reducing resistance torques. In this way, torsional vibration of PDC bits induced by one-way axial percussions could be reduced dramatically. In conclusion, compound percussion drilling techniques with PDC bits can effectively enhance ROP in drilling through hard formations by enhancing cutting depths and reducing torsional vibration.