Kelly drive

A kelly drive refers to a type of well drilling device on a drilling rig

Drilling rig (petroleum)

This article lists the main components of a petroleum drilling rig.The equipment associated with a rig is to some extent dependent on the type of rig but typically includes at least some of the items listed below.-List of items:#Mud tank#Shale shakers...

that 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 turn. When drilling, the drill bit

Drill bit

Drill bits are cutting tools used to create cylindrical holes. Bits are held in a tool called a drill, which rotates them and provides torque and axial force to create the hole. Specialized bits are also available for non-cylindrical-shaped holes....

 is attached at the end of the drill string

Drill string

A drill string on an drilling rig is a column, or string, of drill pipe that transmits drilling fluid and rotational power to the drill bit. The term is loosely applied as the assembled collection of the drill pipe, drill collars, tools and drill bit...

 and thus the kelly drive provides the means to turn the bit (assuming that a downhole motor is not being used).
The Kelly is the square, hexagonal or octagonal shaped tubing and the kelly bushing is the mechanical device that turns the kelly when rotated by the rotary table

Rotary table (drilling rig)

A Rotary table is a mechanical device on a drilling rig that provides clockwise rotational force to the drill string to facilitate the process of drilling a borehole.In the diagram, #20 is the rotary table...

.

A kelly drive refers to a type of well drilling device on a drilling rig

Drilling rig (petroleum)

This article lists the main components of a petroleum drilling rig.The equipment associated with a rig is to some extent dependent on the type of rig but typically includes at least some of the items listed below.-List of items:#Mud tank#Shale shakers...

that 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 turn. When drilling, the drill bit

Drill bit

Drill bits are cutting tools used to create cylindrical holes. Bits are held in a tool called a drill, which rotates them and provides torque and axial force to create the hole. Specialized bits are also available for non-cylindrical-shaped holes....

 is attached at the end of the drill string

Drill string

A drill string on an drilling rig is a column, or string, of drill pipe that transmits drilling fluid and rotational power to the drill bit. The term is loosely applied as the assembled collection of the drill pipe, drill collars, tools and drill bit...

 and thus the kelly drive provides the means to turn the bit (assuming that a downhole motor is not being used).
The Kelly is the square, hexagonal or octagonal shaped tubing and the kelly bushing is the mechanical device that turns the kelly when rotated by the rotary table

Rotary table (drilling rig)

A Rotary table is a mechanical device on a drilling rig that provides clockwise rotational force to the drill string to facilitate the process of drilling a borehole.In the diagram, #20 is the rotary table...

. Together they are referred to as a kelly drive. The upper end of the kelly is screwed into the swivel, using a left-hand thread to preclude loosening from the right-hand torque applied below. The kelly typically is about ten feet longer than the drill pipe segments, thus leaving a portion of newly drilled hole open below the bit after a new length of pipe has been added ("Making a 'connection'.") and the drill string has been lowered until the kelly bushing engages again in the rotary table.
The kelly hose

Kelly hose

A ' is a flexible, steel reinforced, high pressure hose that connects the standpipe to the kelly and allows free vertical movement of the kelly while facilitating the flow of drilling fluid through the system and down the drill string....

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

Standpipe

A standpipe is a type of rigid water piping which is built into multi-story buildings in a vertical position, to which fire hoses can be connected, allowing manual application of water to the fire...

 and allows the free vertical movement of the kelly while facilitating the flow of the drilling fluid

Drilling fluid

In geotechnical engineering, drilling fluid is a fluid used to drill boreholes into the earth. Often used while drilling oil and natural gas wells and on exploration drilling rigs, drilling fluids are also used for much simpler boreholes, such as water wells...

 down the drill string

Drill string

A drill string on an drilling rig is a column, or string, of drill pipe that transmits drilling fluid and rotational power to the drill bit. The term is loosely applied as the assembled collection of the drill pipe, drill collars, tools and drill bit...

.
See Drilling rig

Drilling rig (petroleum)

This article lists the main components of a petroleum drilling rig.The equipment associated with a rig is to some extent dependent on the type of rig but typically includes at least some of the items listed below.-List of items:#Mud tank#Shale shakers...

to view a diagram.