Understanding the Contribution of Primary Stability to Build Aggressive and Efficient PDC Bits

Abstract

A rigorous engineering and research effort combined with targeted field testing has delivered a new generation of PDC technology. This technology is intended to be utilized to drill both the hard-to-drill rock applications and the fast drilling top hole applications around the world. In the fast drilling environment, the bit passes from the softer formation to harder interbedded stringers. In the hard-to- drill rock environments, the bit is drilling at low depths of cut (DOC). In both of these environments, it is critical to the overall performance in both rate of penetration (ROP) and distance drilled that the drill bits exhibit stability that is dependent on how the cutting structure interacts with the formation (primary stability) and keeps the bit from being perturbed when drilling. This paper investigates how increasing primary stability can improve both the aggressiveness and efficiency of the bit and gain performance that cannot be achieved with bits that use damage mitigating features as part of the design methodology to stabilize or otherwise protect the cutting structures in these drilling environments. This paper also outlines a comprehensive product development effort with testing both in a laboratory setting as well as in the field. Using aggressive cutting structures to drill these two environments can increase performance if the bit has a strong primary stability signature as demonstrated by the test protocols used in this development effort. During laboratory testing, the new generation of PDC technology achieved on average 45% faster ROP compared to standard bits while increasing stability and efficiency. This improvement correlated to the field as the new concept bits drilled intervals 30% longer and 25% faster compared with the average performance of runs drilled with PDC bits.