Page 156 - Introduction to Petroleum Engineering

ROTARY DRILLING RIGS 143

FIGuRe 8.5 View up a derrick.

rotary table. The mud hose connects to the side of the swivel as shown in Figure 8.5.
Mud from the pump flows through the hose and swivel before entering the top of the
kelly. The swivel does not rotate, but it allows the kelly and the attached pipe to rotate
while being suspended in the borehole. The bottom end of the kelly is connected
below the rig floor to the drill string, which includes the drill pipe, drill collars, and
the bit. The rotary table spins the KB which rotates the kelly and, by extension, the
drill string. The spinning drill bit breaks up the rock into rock cuttings.
Newer rig systems use a top drive to rotate the pipe string. The top drive can be
hydraulically or electrically powered. The top drive in rotary drilling eliminates the
need for a kelly and rotary table. The top drive reduces the amount of manual labor
during trips and the associated hazards of working on the derrick floor. Top drive rigs
are designed to work with a smaller footprint than other drilling rigs, which reduces
its environmental impact, especially in urban environments where the space available
for well sites is limited.

8.2.4 Drill String and Bits
The drill string consists of the following components: the drill pipe, drill collars, the
drill bit, and optional attachments. Drill collars are heavy‐walled drill pipes that
place weight on the drill bit during actual drilling and that keep the drill pipe in
tension to prevent bending and buckling of the drill pipe. Drill collars are part of the
bottom‐hole assembly (BHA), which includes everything between the drill pipe and