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A roller-cone bit is a drill bit used for drilling through rock, for example when drilling for oil and gas.
A roller-cone bit is a drill bit used for drilling through rock, for example when drilling for oil and gas.
Characteristics
Drilling bits are attachments that are added to the end of a drillstring to perform the cutting necessary to penetrate the many rock layers between Earth's surface and oil/gas reservoirs. Once a hole is drilled, appropriate casings may be inserted to seal the wellbore formation.Howard R. Hughes Sr.
Howard Robard Hughes Sr. (September 9, 1869 – January 14, 1924) was an American businessman and inventor. He was the founder of Hughes Tool Company. He invented the "Sharp–Hughes" rotary tri-cone rock drill bit during the Texas Oil Boom. He is ...
designed and patented the first roller-cone bit in 1909. His design had two rotating cones, but was evolved to a tricone bit (see image above) in the 1930s.
The bits are sub divided into different categories depending on the drilling process, including the type of formation being drilled and the operating conditions anticipated. There are two main categories: roller-cone bits and fixed-cutter bits. Roller-Cone bits are composed of rotating disks called cones. Rock hardness is one of the determining factors taken into account when selecting an appropriate drill bit. The cutting structure of the bits varies according to the rock formation. Softer formations are drilled with a roller-cone bit with widely spaced, long protruding teeth. Whereas harder formations are drilled with closer-spaced and shorter-toothed bits. Roller-Cone bits are versatile and can cut through many formation types.
Soft rock formations include unconsolidated sands, clays, soft limestones, redbeds and shale
Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...
. Medium formations include dolomite Dolomite may refer to:
*Dolomite (mineral), a carbonate mineral
*Dolomite (rock), also known as dolostone, a sedimentary carbonate rock
*Dolomite, Alabama, United States, an unincorporated community
*Dolomite, California, United States, an unincor ...
s, limestones, and hard shale, while hard formations include hard shale, mudstone
Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...
s, cherty limestones and hard and abrasive formations.
The bits are further classified based on their internal bearings. Each bit has three rotating cones and each one will rotate on its own axis during drilling. While the bits are fixed to the drilling rigs, the rotation of the drill pipe will be in a clockwise direction and the roller cones are rotated in an anti-clockwise direction. Each roller cone is rotated on its own axis with the help of the bearing. Again, the bearings are classified mainly into three types: Open bearing bits, Sealed Bearing Bits and Journal Bearing bits.
2. Mitchell, Robert. Miska, Stefan. (2011). ''Fundamentals of Drilling Engineering.'' SPE Textbook Series, vol. 12. Society of Petroleum Engineers.
External links
References
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