At the beginning of the last century, cone bits replaced the position of scraper bits in hard abrasive formation application, but the disadvantage of cone bits in drilling shale and other plastic rock formation is mainly caused by the effect of mud, and as the drilling depth, bottom hole pressure (BHP) and mud gravity increase, balling phenomenon will be more serious.
In order to solve this problem, many drill bit manufacturers have made various improvements to cone bits over the years, but with little effect. Considering that the scraper bit or fixed cutter bit is less affected under this condition, manufacturers began to try to combine the two bits together for a new type of bit.
With the popularization and application of PDC bits and the improvement of PDC cutter technology, PDC bits with fixed cutters have gradually replaced cone bits in various formations. However, in some hard & abrasive formations and complex directional drilling operations, PDC bits can't replace cone bits due to its own performance limitations.
In order to make use of the advantages of both cone bits and PDC bits, Baker Hughes recently developed a new combination bit, called the Kymera combination bit.
This composite bit has two designs: one is a smaller bit with two blades and two cones, and the other is a slightly larger bit with three blades and three cones.
The design of these bits is based on four - and six-blade PDC bits, while the position of the secondary blade is replaced by short-sized cones. In this way, rocks at the central position of the well is breaked by the PDC cutters located on the main blade, while the drilling of the outer part of the well is breaked by the cone and the cutters on the blade.
The rock breaking operation of the outer part of the well is relatively difficult, and the rock breaking effect mainly depends on the cooperation of the cone and the blade of the bit.
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