A top drive is a big motor system which is hoisted in a derrick or mast of a drilling rig. A top drive is a modern rotating system which has been popular for many drilling contractors and oil operators. Top drives can be used on all types of rigs, from truck-mounted rigs to offshore rigs,
A device that turns the drill string. It consists of one or more motors (electric or hydraulic) connected with appropriate gearing to a short section of pipe called a quill, that in turn may be screwed into a saver sub or the drill string itself.
Rotation provided to a drill stem is accomplished by a top drive. Therefore, a Kelly and a Kelly bushing are not required for a top drive system. Moreover, a master bushing and a rotary table serves as support for slip and weight of a drill stem and as a conduit for a drill stem to be raised or lowed into a wellbore.
Since a Kelly is not required, the length of each stand is more than a single joint. Typically, drilling with a top drive can be drilled with a stand of drill pipe which consists of 3 joints of drill pipes. A top drive can drill about 90 ft before making a connection, as opposed to 30 ft like a Kelly. A top drive system allows rotation and circulation while pulling out of a hole (back reaming). However, this operation cannot be performed with a Kelly system.
A top drive is attached to a dolly track acting like a guide rail in a derrick. This allows straight movement up and down while drilling and tripping.
Top drives are a major improvement to drilling rig technology and are a large contributor to the ability to drill more difficult extended-reach wellbores. In addition, the top drive enables drillers to minimize both frequency and cost per incident of stuck pipe.
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