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Stripping is accomplished most easily using the annular preventer.
However, when the surface well pressure is too great, stripping must
be done using two pipe ram preventers placed far enough apart for
external upset tool joints to fit between them. The upper and lower
rams must be closed and opened alternately as the tool joints are
lowered through.
Space between ram preventers used for stripping operations is
provided by a drilling spool. Drilling spools also are used to permit
attachment of high-pressure flow-lines to a given point in the stack.
These high-pressure flow-lines make it possible to pump into the
annulus or release fluid from the annulus with the BOP closed. A
conduit used to pump into the annulus is called a kill line. Conduits
used to release fluid from the annulus may include a choke line, a
diverter line, or simply a flow-line. All drilling spools must have a
large enough bore to permit the next string of casing to be put in
place without removing the BOP stack.
The BOP stack is attached to the casing using a casing head.
The casing head, sometimes called the braden head, is welded to the
first string of casing cemented in the well. It must provide the
pressure for subsequent casing strings placed on the well outlets
are provided on the casing head to reveal the pressure that must be
accumulated between the strings.
The control paper for operating the BOP is usually placed
on the derrick floor. The controls should be marked identifiably
with the BOP stack arrangements used. The panel is used for this
purpose.
The arrangements of the BOP stack vary considerably. It
depends on the magnitude of formation pressures on this area and
on the type of well control procedures used by the operator. API
presents several recommended arrangements of BOP stacks. The
arrangement nomenclature uses the letter “A” to denote the
annular preventer, the letter “R” to denote the ram preventer, and
the letter “S” to denote the spool. The arrangement RSRRA
denotes the usual BOP stack with the ram preventer attached to the

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