Oil and gas operators expect a lot out of the roller cone bits they choose to use in their drilling projects. In addition to producing acceptable rates-of-penetration, operators expect their bits to perform with a high degree of reliability. For a bit to deliver such reliability, it must be engineered to accept tremendous punishment under high loading conditions that want to tear it apart as it crushes the rock in its path to create a borehole. However, because it incorporates moving parts, a roller cone bit inherently poses different challenges to design than a fixed cutter bit. Even when the roller cone cutting structure is optimized for long life, a loss of seal or journal bearing can cause premature bit failure, drastically reducing service life and offsetting any advantage.

(Click image to enlarge) In an effort to move the reliability of its bits to an even higher level, Security DBS initiated an extensive program that resulted in a complete revamping of its roller cone product line. The program included a testing phase in which the revamped bits were tested with hundreds of bit runs, in hundreds of wells. When the performance data results were analyzed, they showed that the effort did indeed produce a more reliable bit capable of meeting operators' challenges head-on. The Reliability Challenge
Bits can fail for a number of reasons, but usually a bit failure is caused by the breakdown of one or more of the internal components. The failure of a key working component can necessitate pulling the drill string and changing the bit. It is no wonder operators seek a bit platform that delivers consistent reliability when drilling in hard rock and/or hostile drilling environments. In terms of bearing performance, reliability is a function of how well the bearing can withstand high axial loads over long runs. This, in turn, greatly depends on how well the bearing seal resists wear which prevents bearing contamination by external debris and cuttings. Similarly, seal reliability depends on an effective pressure compensation system to equalize the differential pressure variations that occur during drilling and which can deform and fail the seal. With all this increased durability making longer service life possible, the bit body must be more robust, with sufficient arm strength to withstand the rigors of extended operation over time.

Addressing these four critical factors, QuadPack™ features, coupled with a balanced cutting structure, minimize vibration and ensure the bit's service life isn't shortened and the sensitive instrumentation package in the bottomhole assembly isn't damaged. Finally, the bit must be manufactured to exacting standards that assure it meets all quality control requirements established during the design and engineering phases. Building Bit Reliability
Increased bearing reliability is at the heart of QuadPack design features. The longevity improvements include: 1. Increased bearing load capacity
Larger size bearings mean larger load-carrying capacity. Optimizing bearing size significantly increased the maximum load bearing capacity of journal bearings, enabling the new bit designs to accommodate application of higher weights and faster rpm loads without failing.

(Click image to enlarge) 2. Greater seal dependability
Seal performance critically affects, and is affected by, several dynamic aspects of bit design. For example, bearing life depends on the load-carrying capacity of the lubricating system grease, which will decrease significantly if poor seal performance allows the grease to become contaminated. With the increased load capacity of new larger bearing designs, there is not only more dynamic loading on the grease – there's more grease, making system integrity even more dependent on seal reliability.

(Click image to enlarge) Seal reliability in turn, is impacted by dynamic pressure regimes that occur during drilling – especially extreme differentials between annular pressure and internal pressure in the lubrication system, which adversely affect seal life. Seal integrity is constantly challenged by annular pressures increasing proportionally with depth, while rising temperatures over depth also increases internal pressure within the lubricating system.

To meet these demands for greater seal dependability, the O-ring of the sealing system was refined for increased thermal- and wear-resistance. Specifically, two aspects were changed. First, the seal material was upgraded to a more temperature-resistant version. The manufacturing process was also changed to eliminate any "seam" in the o-ring by producing the rubber pre-form as an endless piece. This piece is then molded to required high tolerance dimensions. The resulting O-ring design significantly improves seal dependability. 3. More responsive pressure compensation system
To provide a consistent means of quickly achieving pressure equalization under dynamic conditions, a new dome pressure relief system was developed which integrates external pressure compensation with internal pressure relief in a single rubber diaphragm. Compared to previous systems, the new Integrated Diaphragm yields a 50% reduction in the pressure relief point and, perhaps more importantly, an 80% reduction in standard deviation of the vent pressure. This means internal pressure in the sealed portion of the bearing is less variable, with reduced differential to the operating pressures outside the seal, greatly diminishing seal stress and enhancing seal system durability.

(Click image to enlarge) 4. New body forging
Finally, new bit body forgings were generated to produce bit designs with larger, stronger arms and a more durable body capable of providing extended bit service life.

(Click image to enlarge) Manufacturing improvements
Security DBS also focused extensive effort on improving various manufacturing processes which could significantly impact performance, such as re-engineering the final bearing machining process to improve fit and function, dimensional consistency, and optimize journal surface finish. Among others, bearing surface improvement, greasing operation, and parts matching processes were also revamped to manufacture the new bits.

Energy Balanced® Technology
The Security DBS patented Energy Balanced process plays a key role in increasing the reliability of new bit designs. This process, in which bits are balanced by equalizing the load and removal of rock among all three of the bit's roller cones, enhances the service life of the bit and protects the sensitive instrument package in the bottomhole assembly located just behind the bit on the drill string.

(Click image to enlarge) Proven Reliability
Now proven in key basins around the world, bits with the new longevity features are enabling operators to realize the benefits of more robust and reliable roller cone performance even in the face of today's increasingly challenging operating parameters. In Western Canada, hundreds of the new designs were field-tested in a variety of applications over a period of 18 months, delivering an overall 80% reliability rate at 92 hours, compared to 69% by the next-best competitor bit. (Click image to enlarge) In Western Oklahoma and the Texas Panhandle, SDBS 7-7/8-in. and 8-3/4-in. bits demonstrated great reliability. The curves show that the probability of these bits being pulled with all effective seals is better than 80% at 120 hours. This compares with the competitive bits showing only 45% to 55% effectiveness at the same 120-hr mark. In all applications; straight hole, directional and motor, bit records between 2004 and 2005 show that SDBS bits were pulled with seals effective in 91% of the runs while competitor bits were effective in only 80% to 84% of the runs.


(Click image to enlarge) Conclusion
Roller cone bits are typically used for drilling hard rock. These bits must endure considerable axial loading during operation, extreme temperatures, and strong vibrations which create a hostile drilling environment. All these factors affect the life and reliability of the journal bearings that allow the roller cones to cut and crush the rock formation as the bit creates the well's borehole. Protecting the bearing is of paramount importance to the overall performance and reliability of the drill bit. If just one of the three journal bearings fails, the driller must perform a round trip to remove and replace the bit before continuing the drilling process. This can be extremely expensive for operators who are drilling wells that have marginal economics. Newly designed and engineered bits utilizing larger bearing load capacities, greater seal dependability, a more responsive pressure compensation system and new body forgings coupled with Energy Balanced cutting structures and improved manufacturing methods are producing higher bit reliability operators need to meet the faster and deeper demands of today's oil and gas marketplace.