Oil drill bits that are used to create an oil well usually are manufactured as rotating equipment that scrapes, cuts and grinds away rock and other subsurface materials. These drill bits are used to move materials that are located between the Earth’s crust and the oil that lies far beneath the surface. A prime mover and rotating equipment are used in conjunction with the drill bits to rotate the drilling equipment and move it downward. Early attempts at rotating drilling equipment included the use of farm animals walking in circles while attached to a drill pipe and oil drill bit.
The type of drill bit used is generally specific to the material being drilled through and the type of subsurface material that engineers expect to encounter. Oil drill bits can be constructed from materials such as steel, natural diamonds, synthetic diamonds and tungsten carbide. Each bit is made up of at least two cones of teethed, rotating discs that chip away the rock and materials.
Steel-toothed drill bits are the most common types of bits used in drilling for oil. Tungsten carbide can be inserted into the steel bits to add strength and allow movement through stronger materials. Polycrystalline synthetic diamonds can also be added to the tungsten inserts of oil drill bits for moving the bit through stronger rock formations. Where extremely strong rock formations are encountered, a diamond-encrusted drill bit can be used; these drill bits are 40 to 50 times stronger than steel drill bits.
Choosing the correct type of oil drill bit is important in the early stages of drilling through rock and sediments, because it is difficult to change an drill bit after drilling has commenced. Each oil drill bit is attached to a drill string and drill pipes that are assembled in 30-foot (9.1-meter) lengths. To change a damaged or incorrect drill bit for the type of rock encountered, the entire drill pipe, string and bit apparatus must be removed from the well.
When using rotating drill bits, a lubricating fluid must be passed through the drill pipe and onto the drill bit and rock that is being drilled. This is done for several reasons, including the lubrication of the oil drill bit, the removal of rock from the drill pipe and prolonging the life of the drilling equipment. Depending on the type of oil drill bit and rock being drilled, the fluid can include mud that contains chemicals, water and grease, or it can be airless, with gases used to lubricate the drilling equipment. Drilling fluid is important because it moves broken material away from the area of the oil drill bit.