Study on Key Factors Influencing the ROP Improvement of PDC Bits

For the maximization of the efficacy of the polycrystalline diamond compact (PDC) bits in drilling engineering, comprehensive research, including theoretical analysis, laboratory test, case study, and on-site trials, was conducted to investigate how a high weight-on-bit (WOB), a high rotary speed, and other optimized drilling parameters work on the rate of penetration (ROP) and the wear of a PDC bit. Furthermore, the wear mechanism of the PDC bit and the primary cause of the premature failure of the bit were analyzed. The results indicated that: 1) The ROP of the PDC bit was directly and primarily affected by the WOB. When the bit was in an efficient rock-breaking state, the WOB was invariably in a linear relationship with the ROP whether the formation encountered was a conventional one or a hard rock formation. Adding a high WOB over 200 kN into the normal pressurization range of the PDC bit was recommended if the formation encountered was a homogeneous hard rock formation. 2) ROP improvement could be achieved by enhancing the rotary speed. Although the wear of the PDC bit could be aggravated by a high rotary speed, the requirement on a PDC bit to penetrate most formations for a long time at a high rotary speed (400–500 r/min) could be readily met by the quality of the currently available PDC cutter. 3) The ROP of the bit was also affected by cutter density, but not in a direct manner. As long as a dynamic balance among “capabilities to bite into the formation, cut the rock, and evacuate the cuttings in time” was reached, the optimized fast drilling could be achieved even by a PDC bit with a high cutter density. 4) The wear of the PDC bit was less severe under the higher rock-breaking efficiency of the bit. The WOB could be enhanced to improve the ROP and reduce bit wear. 5) Dynamic impact and inefficient rock-breaking were considered the primary causes of the premature failure of the PDC cutter and bit. The key for the PDC bit to achieve efficient penetration was improving rock-breaking efficiency and restraining bit vibration. The above results could be used as a reference for the proper utilization of PDC bits and the innovation of ROP improvement technologies.