polycrystalline diamond (PCD) cutters and drag bit a designs have been substantially improved since their 1972 introduction, and PCD drill bits now are approaching the rolling cone tungsten carbideinsert (TCI) market is terms of revenue size and have surpassed it in terms of economic impact on the drilling industry . These performance improvements have lead to a significant encroachment intothe drill bit market built upon the breakthrough invention of the rolling cone bit by Howard Hughes Sr. Material and design improvements in the last decade, however have now led to the succefulapplication of patented shear cutting PCD elements as well as conventional diamond enhanced crushing style inserts on rolling cone bits. Diamond enhanced rolling cone bits are also a growth market fordiamond elements in drilling.
Failing rock in shear is a more efficient process than by crushing, but most cutting materials can not stand up to the forces generated in the shearing process as rockstrength increases. To take advantage of the unique ability of the PCD cutter to shear rock efficiently, a concerted R&D effort supported by laboratory and field-testing led to the application ofdiamond as a shear cutting element on roller cone bits. A variety of rolling cone shear cutting elements have been developed and successfully commercialized in the last decade.
This paper will discusslaboratory results and increased field performance achieved relative to conventional crushing style diamond and tungsten carbide inserts. The authors will document through case studies increases in rateof penetration (ROP), footage, overall durability, and gauge holding ability in addition to bearing/seal effectiveness that have further reduced drilling costs and served to increase usage ofpolycrystalline diamond elements on roller cone bits. These applications range from such diverse markets as high cost offshore North Sea, to low cost North American land operations.
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