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many cases, fluids in the blowout ignite and reduce the rig to a melted pile of junk.
Blowouts not only waste oil and gas, but also threaten human lives. Obviously,
drilling crews take a great deal of care not to allow blowouts, and, in fact, not many
occur. But, because a blowout is often a spectacular show and human lives are
sometimes lost, a blowout often becomes a media event. Unfortunately, the
impression may linger that blowouts are not the rarity they actually are. In reality,
thousands of wells are drilled every year and very few of them blow out.
A hole full of mud that weighs the right amount—has the correct density—
cannot blow out. But sometimes the unexpected occurs. Because a rig crew is only
human, they can make an error and allow formation fluids such as gas, oil, or salt
water to enter the hole. When formation fluids enter the hole—when a kick occurs—
it makes it presence known by certain things that happen in the circulating system.
For example, the level of mud in the tanks may rise above normal level, or mud may
flow out of the hole even with the mud pump stopped. Alert drilling crews spot these
anomalies (although the anomalies are sometimes subtle) and take steps to control the
well and prevent a blowout.
When crew members discover a kick, they bring blowout preventers, or BOPs
("bee-oh-pees") into play. On land rigs and on offshore rigs that are not floaters, such
as jackups, crew members nipple up (attach) the BOPs to the top of the well below
the rig floor (fig. 189). The preventers are large, high-pressure valves capable of
being remotely controlled.
When closed, they form a pressure-tight seal at the top of the well and prevent
the escape of fluids. On floating offshore rigs, such as semisubmersibles and drill
ships, crew members lower the BOPs to the top of the well on the seafloor (fig. 190).
Two basic types of blowout preventers are annular and ram. Crew members
usually mount the annular preventer at the very top of the stack of BOPs. They call it
an annular preventer because it seals off the annulus between the drill stem and the side
of the hole. An annular BOP can also seal open hole—hole that has no pipe in it. Crew
members typically mount two, three, or four ram-type BOPs below the annular preventer.
Ram preventers get their name from the fact that the devices that seal off the well are large,
rubber-faced blocks of steel that, when actuated, come together much like a couple of

fighting rams butting heads. The two main kinds of ram preventers are blind rams, which
seal off open hole, and pipe rams, which seal off the hole when drill pipe is in use.
Normally, the driller closes the annular preventer first when the crew detects a kick. If it
should fail, or if special techniques are required, the driller uses the ram-type preventers
as a backup.
Closing in the well with one or more of the blowout preventers is only the first
step in controlling the well. To resume drilling, crew members have to circulate the
kick out and circulate in mud of the proper weight. To facilitate circulating a kick, crew
members install a series of valves called the "choke manifold" (fig. 191). A choke is
simply a valve with an opening the size of which a person can adjust (fig. 192). A choke
operator, by using a remote control panel, can vary the size of the choke opening between
fully open and fully closed (fig. 193). To circulate a kick out of the well and pump heavy
mud in, the person operating the choke fully opens it, the driller starts the mud pump, and,

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