Rotary table (drilling rig)
Encyclopedia
Drill string
A drill string on a drilling rig is a column, or string, of drill pipe that transmits drilling fluid and torque to the drill bit. The term is loosely applied as the assembled collection of the drill pipe, drill collars, tools and drill bit...
to facilitate the process of drilling a borehole
Borehole
A borehole is the generalized term for any narrow shaft bored in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water or other liquid or gases , as part of a geotechnical investigation, environmental site...
.
In the diagram, #20 (in blue) is the rotary table. The kelly drive
Kelly drive
A kelly drive refers to a type of well drilling device on an oil drilling rig that employs a section of pipe with a polygonal or splined outer surface, which passes through the matching polygonal or splined kelly bushing and rotary table...
#19, is inserted through the center of the rotary table and kelly bushings, and has free vertical (up & down) movement to allow downward force to be applied to the drill string
Drill string
A drill string on a drilling rig is a column, or string, of drill pipe that transmits drilling fluid and torque to the drill bit. The term is loosely applied as the assembled collection of the drill pipe, drill collars, tools and drill bit...
, while the rotary table rotates it. (Note: Force is not actually applied from the top (as to push) but rather the weight is at the bottom of the drill string
Drill string
A drill string on a drilling rig is a column, or string, of drill pipe that transmits drilling fluid and torque to the drill bit. The term is loosely applied as the assembled collection of the drill pipe, drill collars, tools and drill bit...
like a pendulum on a string.)
Chain Drive
Most rotary tables are chain driven. These chains resemble very large bicycleBicycle
A bicycle, also known as a bike, pushbike or cycle, is a human-powered, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A person who rides a bicycle is called a cyclist, or bicyclist....
chains. The chains require constant oiling to prevent burning and seizing.
Rotary Locks
Virtually all rotary tables are equipped with a rotary lock. Engaging the lock can either prevent the rotary from turning in one particular direction, or from turning at all. This is commonly used by crews in lieu of using a second pair of tongs to makeup or break out pipe.Bushings
The rotary bushings are located at the center of the rotary table. These can generally be removed in two separate pieces to facilitate large items, i.e. drill bits, to pass through the rotary table. The large gap in the center of the rotary bushings is referred to as the "bowl" due to its appearance. The bowl is where the slips are set to hold up the drill string during connections and pipe trips as well as the point the drill string passes through the floor into the wellboreWellbore
A wellbore is any hole drilled for the purpose of exploration or extraction of natural resources such as water, gas or oil where a well may be produced and a resource is extracted for a protracted period of time....
. The rotary bushings connect to the kelly bushings to actually induce the spin required for drilling.
Alternatives
Most recently manufactured rigs no longer feature rotary drives. These newer rigs have opted for top driveTop drive
A top drive 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. It is an alternative to rotary table...
technology. In top drive, the drill string is turned by mechanisms located in the top drive that is attached to the blocks. There is no need for the swivel because the top drive does all the necessary actions. The top drive eliminates the kelly bar and the kelly bushings.