The second line of defense for the workers and the well
to prevent a blowout is the group
of equipment called
blowout preventers (BOPs). BOPs and associated valves are installed on top of the
casing head before drilling ahead after rigging up. These high-pressure safety valves and associated equipment are
designed to shut off the well hole and prevent the escape of the
underground fluids and prevent a blowout from occurring.
After installation, the BOP and associated valves are pressure tested to
insure integrity and proper operations.
The BOP and associated equipment consists of:
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Fig. 1. Blowout preventer stack
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BOP Stack |
Fig. 2. A blowout preventer (BOP)
with one
annular BOP on top and two ram type BOPs
are stacked together with a kill line
valve and a choke line valve.
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A BOP installation could
consist of both
annular and
ram-type BOPs assembled into a stack. Also,
there can be a kill line valve and a choke line valve.
The choke line valve is used to redirect the mud from the well bore
to the choke manifold during a kick.
The kill line valve is used to direct drilling fluid to the BOP during
a kick.
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Annular BOP |
Fig. 3. Annular blowout preventer cutaway diagram showing the head, piston, wear plate,
packing unit, opening chamber, and closing chamber.
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Annular BOPs are designed to form a seal in the
annular space
between the
drill pipe and the wellbore and are usually mounted
at the top of the BOP stack.
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Ram-Type BOP |
Fig. 4. Ram-type blowout preventer
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Ram-type BOPs have rubber faced steel rams that come together
with great force to seal the wellbore. Usually two or more ram-type BOP's are mounted in the BOP stack.
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Choke Manifold |
Fig. 5. Choke manifold
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A
choke manifold is a system of valves used to circulate out a
kick and to circulate mud in of the proper weight. This
device responds automatically to a kick and can prevent a blowout
if properly installed and maintained.
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Accumulator |
Fig. 6. The blowout preventer control systems accumulator showing regulator valves, accumulator bottles, back-up pump (pneumatic), hydraulic reservoir, control manifold, control valves, and pump (electric, gas, diesel).
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The BOP control system, called an
accumulator,
provides the energy to operate the blowout preventers.
This system of consists of:
- Compressed gas bottles,
- Regulator valves,
- Pumps,
- Hydraulic reservoir,
- Control manifold, and
- Control valves.
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