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.
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.
Components of a Top Drive System
The following list is an inclusive explanation of Top Drive System components:
➖Torque Track
➖Optional Swivel
➖Torque Bushing
➖Swivel Sub
➖Extend Frame
➖Quill
➖Mainframe Assembly
➖Load Nut
➖Pipe Handler Assembly
➖Tilt Assembly
➖Stabbing Valve
➖Saver Sub
➖Grabber Assembly
➖Bail Assembly
➖Elevator
Pipe Handler
The Pipe handler consists of:
▪️The Link hanger includes a spring system to clear it off the main shaft while drilling.
▪️Hydraulic cylinders and an actuator arm for the link tilt system to clear the elevator from the drill string while drilling and pick up the pipe from the mouse hole.
▪️Rotation head to enable 360° positioning of the elevator.
▪️A backup tong to enable Makeup/Break – out of the connection with the hydraulic motors.
▪️The backup tong may be hoisted to break out the saver sub and the mud saver valve. It may also be utilized for orientating the drill string at directional drilling.