Page 144 - Drilling Technology in Nontechnical Language

Chapter 5 – RIG SELECTION AND RIG EQUIPMENT 135

bushings, have a tapered profile inside (see fig. 5–20). This taper allows

the drillstring to be suspended in the rotary table by using wedge-shaped
tools called slips (described in the section on drillpipe handling tools later
in the chapter).
On top of the master bushing are four holes spaced 90° apart. These
drive holes allow torque to be transmitted to the drillstring by using a
special square or hexagonal section pipe called a kelly.
During drilling, the kelly (suspended from the traveling block) is
screwed on top of the drillstring. Steel rollers fit on the square or hexagonal

faces, and these rollers are in a steel cage that has four pins underneath.
These drive pins locate in the holes of the rotary table and thus allow torque
to be transmitted from the rotary table to the kelly and subsequently to the

drillstring (fig. 5–21).

Fig. 5–21. Drill oor and rotary table with the drillstring hanging in slips
Photo courtesy of Schlumberger.

With more modern rigs, rotary movement and torque is transmitted
to the drillstring directly from a motor and transmission system that is
suspended from the traveling block. This is called a top drive. It may be

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