Top drive

A top drive is a mechanical device on a drilling rig thatprovides clockwise torque to the drill string to facilitatethe process of drilling a borehole. It is an alternative torotary table. It is located at the swivel place and allows avertical movement up and down the derrick.An advantage of a top drive is that it allows the drilling rigto drill longer sections of a stand of drill pipe. A rotary ta-ble type rig can only drill 30-foot (9.1 m) (single drill piperespectively) sections of drill pipe while a top drive candrill 6090-foot (1827 m) stands (double-triple respec-tively. A triple being three joints of drillpipe screwed to-gether.), depending on the drilling rig type. Having longersections of drill pipe allows the drilling rigs to drill deepersections of the wellbore, thus making fewer connectionsof drill pipe. Another advantage of top drive systems istime eciency. When the bit progresses under a kelly,the entire string must be withdrawn from the well borefor the length of the kelly drive. With a top drive, thedraw works only has to pick a new stand from the rackand make two joints. The savings in time reduces therisk of a stuck string from annulus clogging.Several dierent kinds of top drives exist, and are usuallyclassied based on the Safe Working Load (SWL) ofthe tool, and the size and type of motor used to rotate thedrillpipe. For oshore and heavy duty use, a 1000 shortton, top drive would be used, where a smaller land rig mayonly require a 500.99Motors are available in all sizes, andcome in Hydraulically powered, AC, or DC motors.

1 References Schlumberger Oileld Glossary Tesco Corporation Canrig Drilling Technology LeTourneau Technologies (now Cameron) National Oilwell Varco Warrior Rig GDS International

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