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vibration stresses. Thus, care should be taken to use the
strongest available pipe and to anchor all lines securely
against reaction thrust. Also, some flexibility in the piping
to and from the wellhead is required.
The weight of valves and fittings should be supported on
structural members so that bending stresses are not created in
the piping. Because of fluid abrasion, the number of bends
should be minimized. The bends required should be sweep-
turn bends rather than sharp "L" turns, or has an abrasion-
resistant target at the point of fluid impingement in the bend.
API8 presents several recommended choke manifold
arrangements for 12960, 32400, 64800, and 97200 psi working
pressure systems. In addition to these recommendations, well
operators have developed many other optional designs. The
arrangement selected must be based on the magnitude of the
formation pressures in the area and the well control procedures
used by the operator. In this arrangement, a hydraulically
controlled valve separates the BOP stack from the choke manifold.
This valve normally is closed during drilling operations to prevent
drilling mud solids from settling in the choke system. The controls
that operate this valve are placed on the BOP control panel so
that the BOP can be operated easily. Two adjustable chokes
(Fig. 12.4) would allow kick circulation to continue in the event
one of the adjustable chokes fails.
A mud gas separator permits any produced formation gases
to be vented. Also, valves are arranged so that the well fluids can
be diverted easily to the reserve pit to prevent excessive pressure
from fracturing shallow formations below a short casing string.
The kill line permits drilling fluid to be pumped down the
annulus from the surface. This procedure is used only under special
circumstances and is not part of a normal well control operation.
The kill line most frequently is needed when subsurface pressure
during a kick causes an exposed formation to fracture and to begin
rapidly taking drilling fluid from the portion of the hole.
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