A top drive
is a mechanical device on a drilling rig
A drilling rig is a machine which creates holes or shafts in the ground. Drilling rigs can be massive structures housing equipment used to drill water wells, oil wells, or natural gas extraction wells, or they can be small enough to be moved manually by one person...
that provides clockwise rotational force to the 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
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...
. It is an alternative to rotary table
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...
. It is located at the swivel
A ' is a mechanical device used on a drilling rig that hangs directly under the traveling block and directly above the kelly drive, that provides the ability for the kelly to rotate while allowing the traveling block to remain in a stationary rotational position while simultaneously allowing the...
place and allows a vertical movement up and down the derrick.
An advantage of a top drive is that it allows the drilling rig to drill longer sections of a stand of drill pipe. A rotary table type rig can only drill 30'-60' (double-triple respectively) sections of drill pipe while a top drive can drill 60' to 90' stands, depending on the drilling rig type. Having longer sections of drill pipe allows the drilling rigs to drill deeper sections of the wellbore, thus making fewer connections of drill pipe.
Several different kinds of top drives exist, and are usually classified based on the "Safe Working Load" (SWL) of the tool, and the size and type of motor used to rotate the drillpipe. For offshore and heavy duty use, a 1000 short ton, top drive would be used, where a smaller land rig may only require a 500. Motors are available in all sizes, and come in Hydraulically powered, AC, or DC motors.
A top drive
is a hydraulic or electric motor suspended in the derrick (mast) of a drilling rig, which rotates the drill string and bit and is used in the actual process of drilling the well. Using a top drive
eliminates the need for the traditional kelly and rotary table and reduces the amount of manual labour and associated hazards that have traditionally accompanied this task. For drilling contractors and producers, utilizing top drive technology translates into increased efficiency in its operations. Top drive ratings are based on the safe static hook load, this rating relates to the main thrust bearing (usually the weakest link). Top drive ratings of 500 short tons typically have an API rating lower than 500T, due to required calculations of rotation with a percentage of rated load.