Page 65 - Air and Gas Drilling Manual

Chapter 2: Surface Equipment 2-15
rams on the top and a blind ram on the bottom. The two pipe rams allow some
flexibility in carrying out well control when drilling deep wells with a tapered drill
string and when placing a liner string in an air or gas drilled well. This BOP stack
is fitted with a rotating head flange connected to the top pipe ram blowout preventer.
This stack can be configured for the recovery of oil and natural gas deposits with
static bottomhole pressures of up to 5,000 psi.
The annular-type blowout preventer can also be used in a BOP stack (see Type 3
in Figure 2-7). An annular preventer is hydraulically operated. Figure 2-12 shows a
cut-a-way view of a typical annular preventer. The closing of the preventer is
actuated by hydraulic pressure. This hydraulic pressure forces the operating piston
upward against a pusher plate (see Figure 2-12). The pusher plate in turn displaces
(compresses) an elastomer donut inward to close and seal on the outer surface of drill
pipe, drill collar, casing, or liner. Utilizing an annular preventer in conjunction
with ram blowout preventers greatly increases well control flexibility and general rig
safety when drilling with air and gas drilling fluids. The Type 3 BOP stack in
Figure 2-7 is configured with twin ram-type blowout preventer on the bottom (pipe
ram on top and blind ram on the bottom), an annular preventer flange connected to
the top of the twin ram preventer, and a rotating head flange connected to the top of
the annular preventer. This BOP stack can be configured for the recovery of oil and
natural gas deposits with static bottomhole pressures of up to 10,000 psi.

Figure 2-12: Typical annular blowout preventer (courtesy of Cooper Cameron
Corporation).