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114 Part II Gas Drilling Systems

Rotating Head

Annular BOP

Pipe Rams

Blind Rams

Drilling Spool

Figure 5.8 A typical BOP stack with a rotating head.

It diverts the returning gas stream to the blooey line so normal operations
at the drilling floor can be performed safely. The rotating head is installed
on the top of the blowout preventor (BOP) stack (Figure 5.8).

5.3 DOWNHOLE EQUIPMENT

The downhole equipment used in gas drilling is similar to that used
in liquid drilling, with the exception of air hammers and flat-bottom bits.
Using a combination of these tools allows faster drilling with less weight
on bit. These tools are used for drilling extremely hard formations and
for drilling surface rocks in mountains before drill collars are added to
obtain adequate weight on bit. Sometimes they are utilized to drill
straight holes in crooked hole areas with low weight on bit. They can
also be used to drill horizontal holes where the weight on bit is limited
due to high torque and drag.
Figure 5.9 shows an air hammer with a flat-bottom bit. The gas flow
path is self-controlled by a valve inside the hammer, which moves the
piston to produce 1,200 to 1,800 strokes per minute. The piston hits the
top of the bit and generates enough force on the bottomhole that the bit