In 1987, the IADC adopted an improved Rock Bit Dull Grading System. Although it was modeled after the previously used T-B-G System, it was expanded to provide a much clearer "mental picture" of a dull bit. This paper documents the changes from the 1987 version to the 1992 IADC Dull Grading System. Since the changes are minor, they are listed at the beginning of the paper. Additionally, for those needing more detail, the entire 1992 IADC Dull Grading System is presented. CHANGES FROM 1987 * Outer Cutting Structure: Definition will change to "All cutting elements that touch the side of the hole".*Reasons Pulled Add: "LIH" - for "Left in Hole"*Bearing Grade Add: "N" - for "Not Able to Grade"*Location: "G" represents gage area, replacing "H".*IADC bit topics also updated in 1992 include IADC Classification and Fixed Cutter Dull Grading. Introduction The use of dull bit evaluation methods represents a key step in the advance of rock bit technology. Historically, a driller would learn through experience how to examine a "dull" to determine what type of bit to run next, and how it should be run (WOB, RPM, etc.). This was part of the art that separated the best drillers from the rest. An industry wide effort began years ago to teach the art of bit wear analysis to a broader range of personnel so that dull bit evaluation would become an integral part of daily drilling practice. General guidelines were established in the mid-1950's for relating typical bit wear patterns to the possible causes and remedies. This approach was helpful but limited by the lack of a common vocabulary for describing bit wear and documenting the dull condition in drilling reports. Meanwhile, basic bit performance studies produced a greater appreciation for the economic impact of bit wear and its close relationship to bit selection and operating practices. An industry standard for reporting bit wear was clearly needed. The Weight/Speed/Penetration Sub-Committee of the American Association of Drilling Contractors (AAODC) established the first dull grading standard in 1961. P. 819^
A significant research and development effort plus extensive laboratory andfield tests have resulted in a new generation of roller cone bits, namely anenergy balanced roller cone bit. An energy balanced roller cone bitincorporates three patented features:balanced cutting structure,optimized tooth orientation, andoptimized anti-tracking mechanism. This paper details the principles of these three features and their application torock bit design. Field performance of energy balanced bits is evaluated by rateof penetration, footage drilled, durability of cutting structure, andreliability of bearing/seal system. Significant performance improvement hasbeen observed in the field. Introduction Optimum combination of drilling efficiency (the rate of penetration) anddurability (the bit life) for specific formations is always an objective in thedesign of a roller cone bit. Durability of a roller cone bit is determined bythe shorter of cutting structure durability and seal/bearing durability. Thispaper focuses on the design of bit cutting structures in order to improvedrilling efficiency and durability and to extend bearing/seal life. However, the design of a seal/bearing system is not the topic of this paper. Drilling efficiency is directly associated with the cutting structure. Fromthe aspect of bit design, a roller cone bit may be designed to drill very fastfor a given formation by increasing the tooth extension, reducing the number ofteeth, increasing the cone offset, etc. However, such a design may lead to veryearly damage of the cutting structure such as insert breakage and insert loss.From the aspect of bit application, a roller cone bit may drill fast byapplying high weight on the bit and/or by applying high rotational speed. Butif the energy level applied to bit is too high, not only cutting structures, but also bearings and arms may fail unexpectedly. Usually it is very hard to design a cutting structure of a roller cone bitthat has high drilling efficiency and high durability simultaneously. Themodifications of roller cone bit design are based on years of experience inevaluating bit run records and dull bit conditions. The best solution so far isto develop a compromise between efficiency and durability. Since drill bits arerun under inhospitable conditions, it is usually difficult to determine whatcaused a bit failure. It is also difficult to evaluate a bit's performance inthe field because drilling conditions vary from well to well. Anotherdifficulty is to identify design weaknesses based on performance of individualbits. Obviously, cutting structure design plays a key role in roller cone bitperformance. There must be an optimized cutting structure that not onlyincreases rate of penetration but also increases cutting life and extendsseal/bearing life. In this paper, the principles of three patented technologies, namely,balanced cutting structure,optimized tooth orientation, andoptimizedanti-tracking mechanism, are detailed. The effects of these technologies on bitdrilling efficiency and bit durability as well as on seal/bearing life arediscussed. It is well known that seal/bearing durability can be described byreliability curves expressed as a function of bit life1. In order tosystematically evaluate the performance of energy balanced bits, the durabilityof cutting structures is also obtained by using information from bit dullconditions. Thus, the reliability of a roller cone bit is appropriatelyestablished by the combined reliabilities of both the cutting structure and theseal/bearing system. Energy Balanced Roller Cone Bit Balanced Cutting Structure Roller cone bits may have one, two, three, or four cones. However, in thispaper the discussion will be focused only on roller cone bits with three cones.Each cone removes a part of formation and takes a part of the weight on a bit.If all three cones remove the same volume of formation during drilling, thenthe bit is volume balanced. When each of the three cones is subject to the sameforces, then the bit is force balanced. Fig. 1 depicts three major forces acting on each cone duringdrilling. If a roller cone bit is both volume and force balanced, then the bitis called an energy balanced bit.
Summary Over the years, a variety of problems with PDC bit design and application has been well documented. The industry has discovered that many of these inherent problems can be explained as being caused by ‘bit whirl’. The goal of most PDC manufacturers and the subject of this paper is the development of a better-performing, ‘whirl resistant’ PDC bit. Similarly, the goal for most operators is the decreased costs which are a direct result of the effective application of such bits. The possibility of decreased cost due to improved performance has led to most operators focusing on their PDC operations in order to lend assistance to the industry and to bit manufacturers in all phases of bit development and application. This paper discusses a cooperative development effort between operators and manufacturer to effectively apply advanced concepts to the design, manufacture and application of a new series of PDC bits in South Texas. The paper describes PDC design concepts such as force balanced cutting structures, asymmetric blade layouts, spiral blade designs, and tracking cutter arrangements. Such design principles are shown to be effective in countering the destructive effects of ‘bit whirl’ and allow the PDC bit to be utilized in harder formations. A presentation of performance data, operational details, and economic analyses concerning the use of these bits in several south Texas fields is given. The cooperative effort between operators and manufacturer to develop the advanced PDC concepts is discussed. Introduction This paper presents the results of a project to develop PDC bits for specific application in the intermediate section of the Wilcox (Lobo Trend) area of South Texas (Figure 1). The overall goal of the project was to improve PDC bit performance and, thus, reduce drilling cost. The project involved a joint development effort between the operators and the bit manufacturer. The operators' drilling departments worked jointly with the bit design and application engineers to develop PDC bits for their specific applications. The direct benefit of a joint development effort to the operators was the significant savings that would be realized as a result of improved bit performance. Over the past decade, it has been well documented how PDC application in the production section of the Lobo Trend has reduced drilling costs by as much as 30%. These savings were first realized in the early 1980's when the standard practice was to displace the water base mud with an invert-emulsion oil mud. The use of oil mud in the production section of the Lobo Trend proved extremely beneficial to the performance of PDC bits. The synergism between PDC bits and oil mud resulted in increased rates of penetration, increased bit life and decreased drilling cost. The cost savings were so dramatic that the use of oil mud and PDC bits in the production section became the standard practice at the time. Recent work has led to the development and current use of an ROP-enhanced water base/terpene mud system in the production section.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractBased on computer drilling simulation results, a new, unique roller cone bit has been developed 1 . All the teeth on this new bit are oriented optimally such that the leading face of the elongated crest of a tooth is perpendicular to its trajectory during interaction with a formation. This paper describes the computer model, the calculation procedure for determining the trajectories of the teeth, and the method for designing the new bit. Laboratory and field tests have shown that the new bits drill up to 25% faster and longer than the same type of bits with conventional tooth design.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.