With development of a more reliable bearing system used in Energy Balanced™ bits, Security DBS for the first time offers a line of high performance drill bits specifically designed and manufactured to take full advantage of optimized roller cone cutting structures. The new upgraded bit line is supported by a platform that increases reliability by more than half, enabling users to benefit fully from the increased penetration rates and durability of Energy Balanced bits.
The dramatically improved bit platform was developed through a year-and-a-half long study in which a series of design improvements, material enhancements, and manufacturing process advances were identified and field-tested. At conclusion of the project in October 2003, the resulting improvements exceeded project goals, with reliability of high performance Energy Balanced bits increased by more than 50 percent.
Advantages of energy balancing
Energy Balanced bits are designed so that each cone is subject to substantially the same magnitude of forces, making the bit "force balanced". In addition, each cone removes a near equal volume of formation while drilling, making it "volume balanced". To maximize rock removal rate, a patented cutter positioning algorithm optimally positions and orients cutters, improving drilling rates and reducing the risk of damage to the bit cutting structure.
Threats to bit performance
Bearing life depends on the capability of the grease in the bit lubricating system to carry dynamic bit loads while drilling. As grease is contaminated, its ability to carry the often-extreme loads decreases progressively. Therefore, prolonging the ability of the bit seal to prevent contamination of grease is fundamental to sustaining bearing life.
Preventing encroachment of contaminants into the bearing/seal system can become especially problematic in projects designed to penetrate high temperature, high-pressure downhole environments. High temperatures and/or abrasive fluids or particles in the well bore can substantially degrade the behavior of seal materials in response to downhole dynamic forces.
Seal reliability is also impacted by the dynamic pressure regimes that affect the bit during drilling operations. In particular, seal life is adversely impacted by extreme pressure differentials between annular pressure and internal bit lubrication system pressure. Annular pressures acting on the exterior of the bit increase proportionally with increasing depth. At the same time, heat increases with depth, thereby raising the lubricating system pressure inside the bit, as well as challenging the integrity of the seal material.
Bit bearing reliability project
The project was divided into four sub-projects: seals, bearings, pressure compensation, and manufacturing. The goal was to consistently achieve 80 percent reliability of bit seals after 120 hours of drilling in standard downhole conditions, a level that would challenge Security DBS to improve reliability by 50 percent.
The 7-7/8 inch bit was chosen because its widespread use in the U.S. and Canada would provide the greatest initial benefits from reliability upgrades. Also, the large, diverse well population allowed Security DBS to confirm reliability improvements through real-world applications at literally hundreds of well sites. Data was taken directly from the field and analyzed to establish the baseline reliability of high-performance roller cone bits marketed by major oilfield service companies. These baselines were then used for comparison against reliability improvements.
A further objective was to eliminate any variations in manufacturing that could lead to deterioration and failure of bit platform components. Among the issues addressed were bearing surface finish, bearing geometry consistency, stricter quality control of specific assembly processes, elimination of various heat processes, and parts matching.
Manufacturing improvements were continuous throughout the course of the project, while design and materials changes to bearings, seals and pressure compensation systems were evaluated over time in a statistically useful number of field applications.
Resulting reliability improvements
A pattern of continual improvement was established during field tests, and as the reliability project concluded, two new bearings were selected, both of which included better sealing of the lubrication system. Specifically, two aspects of the o-ring seals were changed during the project. The material was upgraded to be more temperature-resistant and the manufacturing process for producing the o-ring seal was improved.
In addition, Security DBS developed a new dome pressure compensation system that provides a consistent means of achieving pressure equalization under dynamic conditions. The new system combines external pressure compensation and internal pressure relief into one integrated rubber diaphragm. Laboratory tests indicate that the new integrated pressure compensation system reduces relief pressure by 50 percent, thereby reducing the differential to the operating pressures working on the outside of the seal. More importantly, it achieves an 80-percent reduction in standard deviation of the relief pressure, significantly reducing internal pressure variation in the sealed portion of the bearing.
Project surpasses reliability targets
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Manufacturing enhancements instituted as a result of the reliability project currently are being implemented at the Security DBS Bit Technology and Manufacturing facility in The Woodlands, Texas. Although the project focused on 7-7/8" insert bit development, the impact will be felt across the entire product line as changes are incorporated into other popular sizes of Security DBS roller cone bits.