drilling bitBit is the cutting tool used in drilling. On a cable tool rig a percussion bit is used, The percussion bit is a pointed or wedge-shaped weight that pulverizes the rocks on the bottom of the well as the bit is raised and lowered. On a rotary rig a rotary bit is used The rotary bit is turned by the drillstring or downhole motor to chip and flake the rocks at the bottom of the well. The most common rotary bit is the rock or roller-cone hit that has two, three, or four rotating cones on the bottom of the bit. The tricone bit with three cones is most common. The tricone bit has three legs welded to a shank. The legs hold journals around which bearings rotate ro allow the cone on each leg pin to turn.
Roller-cone hits are either a) milled tooth-steel teeth ur b) insert button bits. Drag bits are rotary bits that have blades that rear into soft formations. Diamond hits have no moving parts and have diamonds that are imbedded into the matrix on the bottom and sides of the bit.

Diamond bits are used fiat drilling through hand rocks and coring. A polycrystalline diamond hit (PCD hit) is a drag hit with blanks of manmade polycrfstalline diamonds. Regular bits have an opening in the center of the hit body for drilling fluid. Some are full bore openings and {ithers are ported The jet hit has fluid courses through the body. of the bit or between the cones that are equipped with let nozzles. On a conventional tricone bit, there are noules located between the cones The drilling fluid jets out the nozzles and impacts directly on the teeth of the cones of a roller-cone hit. Extended nozzle bits have elongated fluid paths to reduce the distance herween the nozzle exit and the buttom of the hole. Rotary cone drill bits are good from 8 to 200 hours of rotating and wear out after an average of 24 hours of rotating.

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