Hybrid Bits Offer Distinct Advantages in Selected Roller-Cone and PDC-Bit Applications

Early concepts of hybrid drill bits go back to the 1930s, but the development of a viable drilling tool has become feasible only with the recent advances in polycrystalline-diamond-compact (PDC) cutter technology. This paper describes a new generation of hybrid bits that is based on proven PDC-bit designs with rolling cutters on the periphery of the bit. Laboratory and field results will be presented that compare the performance of hybrid bits with that of conventional PDC and roller-cone bits. A hybrid bit can drill shale and other plastically behaving formations two to four times faster than a roller cone bit by being more aggressive and efficient. The penetration rate of a hybrid bit responds linearly to revolutions per minute (RPM) unlike that of roller-cone bits, which exhibit an exponential response with an exponent of less than unity. In other words, the hybrid bit will drill significantly faster than a comparable roller-cone bit in motor applications. Another benefit is the effect of the rolling cutters on the bit dynamics. Compared with conventional PDC bits, torsional oscillations are as much as 50% lower, and stick/slip is reduced at low RPM and whirl at high RPM. This gives the hybrid bit a wider operating window and greatly improves toolface control in directional drilling. The hybrid drill bit is a highly application-specific drill bit aimed at (1) traditional roller-cone applications that are rate-of-penetration (ROP) limited, (2) large-diameter PDC-bit and roller-cone-bit applications that are torque or weight-on-bit (WOB) limited, (3) highly interbedded formations where high torque fluctuations can cause premature failures and limit the mean operating torque, and (4) motor and/or directional applications where a higher ROP and better build rates and toolface control are desired.