Used to rotate the drill string during the drilling process, the top drive is a motor that is suspended from the derrick, or mast, of the rig. These power swivels boast at least 1,000 horsepower that turn a shaft to which the drill string is screwed. Replacing the traditional Kelly or rotary table, the top drive lessens the manual labor involved in drilling, as well as many associated risks.
A top drive is comprised of one or more electric or hydraulic motors, which is connected to the drill string via a short section of pipe known as the quill. Suspended from a hook below the traveling block, the top drive is able to move up and down the derrick. Many times, slips are still employed on a rotary table to ensure the drill string does not fall down the well.
Chosen both for increased safety and efficiency, top drives provide several key benefits:
- A top drive is capable of drilling with three joints stands, instead of just one pipe at a time.
- Top drives typically decrease the frequency of stuck pipe, which contributes to cost savings.
- A top drive allows drillers to more quickly engage and disengage pumps or the rotary while removing or restringing the pipe.
- Top drives are also preferable for challenging extended-reach and directional wells.
Reducing risk and increasing safety during the drilling process, top drives remove much of the manual labor that was previously required to drill wells. Many times, top drives are completely automated, offering rotational control and maximum torque, as well as control over the weight on the bit.
Top drives can be used in all environments and on all types of rigs, from truck-mounted units to the largest offshore rig. Although top drives can be used on both onshore and offshore rigs, there are some differences between the two. For example, on an offshore rig, the top drive travels up and down the vertical rails to avoid the mechanism from swaying with the waves of the ocean.