Depending on who you ask in the purchasing cycle, the drill bit may be considered an expendable commodity to be bulk delivered to the rig site, or an indispensable high tech tool to be carefully selected and applied. The evidence would overwhelmingly support the latter as the general view of the drilling community.
While drill bits typically constitute a very small percentage of the overall drilling costs, their effect on well economics is profound in almost all cases. The classic cost per foot equation for costs incurred while drilling clearly demonstrates the leverage of rate of penetration (ROP) and bit life (BL). If either of these fundamental elements is seriously compromised, the resulting cost affect can be dramatic, particularly as rig costs, and depth increase.
In recent years, numerous other economic drill bit factors have been recognized for their impact on the overall costs of the well. Hole tortuosity and hole quality can have profound effects on cementing, casing difficulty and log quality. Drill bit directional tendencies and steerability can dramatically affect the costs of a directional well and the ability to steer to targets in the reservoir. Drill bit stability and drilling dynamics can affect the life of the bit, the life of other tools in the bottomhole assembly (BHA), as well as affecting data acquisition and data transmission integrity.
All of these factors have contributed to the increasing level of sophistication seen in today's drill bit technology. These same factors, combined with other emerging technologies in exploration, will continue to push the venerable drill bit into frontiers yet to be determined.
Technology begets technology
Improvements in drilling technology tend to spawn development throughout the industry. Limitations in cable tool drilling led to the invention of the rotary drilling system, which led to the development of rotary bits for drilling. The never-ending search for petroleum resources led to deeper more challenging wells, which demanded better rigs, fluid systems, and naturally, better bits to take advantage of these systems. The pattern repeats itself throughout the history of petroleum exploration as innovation in one area leads to the complementary innovation in others.
There have been several major milestones in drill bit development and hundreds of minor ones since the introduction of the rotary drill bit. The majors, in my opinion, influenced the development of sealed journal bearing rock bits with high-pressure fluid jets. These bits ushered in an era of major changes in drilling practices such as recognition of the importance of hydraulics in drilling, and the ability to turn the rotary at much higher speeds while maintaining good bit life.
Another major development was the introduction of the polycrystalline diamond compact (PDC) bit utilizing man-made diamonds as cutting elements. The efficient shearing action of these products, combined with the inherent reliability of the bit, allowed for extremely high ROP and bit life, particularly in the recent sediments found in most basins of the world. PDC bits have had a dramatic effect on the economics of drilling due to this multi-fold impact on the cost per foot equation.
There have been hundreds of intermediate steps in this evolving technology, some driven by the evolution of bits themselves, and some driven by the introduction of new drilling technology. One only need think of the introduction of downhole motors and top drives, which spawned high-speed bit technology; 3D seismic, which spawned steerable assemblies and steerable bits; or re-entry technology, which spawned slimhole systems, coiled tubing drilling, and all the slim hole bit technology.
New metallurgical processes have allowed the once lowly mill-tooth bit to re-emerge as a cost-effective tool in the driller's arsenal. New carbide materials and synthetic diamonds have, in some cases, doubled the performance of rock bits and PDC bits. Development of special cutters combined with engineered features is allowing PDC bit usage with motors. One of the oldest bit technologies, impregnated diamond technology, has re-emerged with the help of modern metallurgy to provide solutions for some of the toughest drilling applications in the oilfield.
Which comes first, the drilling technology pulling the bit technology, or vice-versa, makes little difference as long as these complementary systems continue to lower the finding costs and improve the overall ability to harvest the reservoir.
End of the technological road?
The question of where this development ends is a frequent query, particularly during the downside of one of our famous business cycles. For years, I have heard the rumblings of the demise of one technology or another, or the relegation of that technology to the dreaded commodity status.
Drilling fluids can never improve, yet synthetic muds came into play. Rotary drilling speeds are at the practical limit, but top drives and high-speed motors changed all that. Cheap reliable electronics have allowed us to push the digital world into areas we never imagined 20 years ago, and developments today will allow us to push our current technologies in directions we can only imagine.
As long as there is a quest for cheap reliable energy resources, the industry will continue to innovate and change. We will not accept a 30% reservoir recovery rate, if we believe that 50% is achievable. The drill bit will continue to evolve, improve, and perhaps, be revolutionized during this process. You won't find it next to the flour in the grocery store any time soon.
John Deane
Schlumberger Reservoir Development - Reed-Hycalog
Houston
