Kelly Drive Versus Top Drive System

comparison of rotary drilling rig kelly drive and top drive (TDS) systems

There are two drive systems used on rotary drilling rig. These are Kelly drive and top drive system. In this post we will go through of  kelly drive versus top drive system. Top drive system is also known as TDS. 


In kelly system, Rotary table provide rotation. Whereas in  TDS, String is rotated with TDS motor.

Kelly drive is Cheaper but also slow , inefficient and unsafe. Whereas . Top drive system is Expensive but Fast, efficient, and safe.

Kelly drive system is capable to drill with one single drill pipe.  On other hand TDS is capable to drill with drill pipe stand. One  drill pipe stand is made of three drill pipe joints together.

While tripping if needs back reaming & circulation, need to Pick up  kelly with swivel from rat hole and connect with string.Its very convenient to connect TDS and back ream with circulation at any point.

Kelly Take longer time to make connection. TDS take less time to make connection.

For tripping, Kelly must be rack back with swivel in rate hole on rig floor. TDS keep hanging all time  with travelling block & hook while tripping.

Kelly is old drive system. Whereas  TDS is new drive  system.

Kelly is not round pipe reduce life of BOP rubber element. In TDS drill pipe are completely      round, better for BOP element.

Kelly need two case hole on rig floor, Rate hole & mouse hole. In case of TDS we need only mouse   hole on rig floor.

In Kelly system crew have to operate elevator manually, so less safety for rig crew. TDS have hydraulic  system to move links and elevator, so TDS have more safety.

In Kelly drive, bit is off bottom equivalent to Kelly length when connect another pipe for drilling. In TDS system bit almost on bottom, when make new drill pipe stand. 

To see  video related kelly drive versus click here

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