Kelly drive

A kelly drive refers to a type of well drilling device on a "drilling rig" which employs a section of pipe with an outer surface that is square, hexagonal or octagonal which passes through the kelly (mating) bushing and rotary table. This bushing is rotated via the rotary table and thus the pipe and the attached drill string turns. When drilling, the drill bit is attached at the end of the drill string and thus the kelly drive provides the means to turn the bit.

The Kelly is the square, hexagonal or octagonal shaped tubing and the rotary table and kelly bushing is the mechanical device the turns the kelly, and together they are referred to as a kelly drive. They are an integral part of each other and each would be nearly useless without the other.

The kelly hose is the flexible, high-pressure hose that is connected to the kelly (or more specifically to the gooseneck on the swivel above the kelly) from the standpipe and allows the free vertical movement of the kelly while facilitating the flow of the drilling fluid down the drill string.

See "Drilling rig" to view a diagram.