Innovative Approach to Maximizing Completion Drill Bit Longevity

For almost a decade, the predominant completion drill-out bits utilized to drill composite frac plugs were roller-cone (RC) bits incorporating "hybrid" cutting structures. RC hybrid cutting structures consist of various layouts incorporating a combination of milled teeth (MT) and tungsten carbide insert (TCI) cutting elements that exhibit known trade-offs regarding longevity and performance. The objective of this paper is to illustrate how practicing engineers can, and should, question status quo to overcome traditional design/performance limiters. Extensive analysis of hybrid RC dull bits and performance data was conducted with the goal to advance RC completion drill bit longevity and performance while reducing non-productive time (NPT). Through quantifying and classifying cutting structure damage across 30 RC hybrid drill bits, data collected clearly illustrated which portions of the bit profile and cutting elements were sustaining the most damage. The data indicated commonly accepted hybrid RC designs display an inherent weakness that would require questioning common beliefs about completion RC bit design and manufacturing methodologies. A new bit design was developed and extensively field tested. The results of the dull bit evaluation indicated the MT are inherently less robust and result in more performance limiting cutting structure damage. The MT have been utilized as a standard due to industry acceptance, manufacturing limitations associated with implementing the more robust TCI's in all portions of the bit profile and perceived benefits with MT geometry. Implementing full TCI coverage to mitigate cutting structure damage required rethinking longstanding manufacturing methods and cutting element selection that have been accepted as industry standards. Changes in manufacturing methodology required increasing surface hardness of the cone face around TCI's to avoid loss due to interaction with slip debris and/or weakened TCI retention due to erosion. This change required a substantial and challenging shift in heat-treating methods and manufacturing workflow. Further changes were made to the TCI geometries in the new design to ensure the aggressiveness needed to fail soft composite plug materials into small debris sizes was equivalent or better than the MT cutting elements. The manufacturing, material and geometric changes resulted in a solution that contradicted previous trade-off understandings regarding completion drill bits by simultaneously improving durability and aggressiveness. The work exemplifies the importance for practicing engineers continuously to question status quo in pursuit of continuous improvement even when faced with longstanding beliefs and/or methodologies. Furthermore, the findings from the project give insight into completion drill-out trends and opportunities to reduce NPT and improve efficiency.