Abstract

Early concepts of hybrid drill bits go back to the 1930's but the development of a viable drilling tool has only become feasible with the recent advances in polycrystalline diamond compact (PDC) cutter technology. This paper describes a new generation of hybrid bits that are 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 RPM unlike roller cone bits, which have an exponential response with an exponent of less than one. In other words, the hybrid bit will drill significantly faster in motor applications. Another benefit is the effect of the rolling cutters on bit dynamics. Compared to conventional PDC bits, torsional oscillations are as much as 50% lower; stick/slip is reduced at low revolutions per minute (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 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 rate of penetration and better build rates and toolface control are desired.

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