Drilling Bit Types and Drilling Bit Selections

Currently in the drilling industry, there are two main categories of drilling bits: rolling cutter bits and fixed cutter bits. Plus, bit sizes vary from 3-7/8 inch to 36 inches.

 Rolling Cutter Bits

Rolling cutter bits, which some may also call roller cone bits or tri-cone bits, have three cones. Each cone can be rotated individually when the drill string rotates the body of the bit. The cones have roller bearings fitted at the time of assembly. The rolling cutting bits can be used to drill any formations if the proper cutter, bearing, and nozzle are selected.

There are two types of rolling cutter bits which are milled-tooth bits and tungsten carbide inserts (insert bits). These bits are classified by how the teeth are manufactured:

1. Milled-tooth bits


(Mill Tooth Bit)

Milled-tooth bits have steel tooth cutters, which are fabricated as parts of the bit cone. The bits cut or gouge formations out when they are being rotated. The teeth vary in size and shape, depending on the formation. Teeth of the bits are different depending on formations as follows:

Soft formation: The teeth should be long, slender and widely spaced. These teeth will produce freshly broken cuttings from soft formations.

Hard formation: The teeth should be short and closely spaced. These teeth will produce smaller, more rounded, crushed, and ground cuttings from hard formations.

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