Page 120 - Well Control for Completions and Interventions

112 Well Control for Completions and Interventions

If more than one no-go nipple is needed for the same size tubing
string, then the no-go diameter must be progressively reduced with
depth. If a large number of nipples are required, the cumulative reduction
can be significant, seriously reducing the through bore of the completion.
This cumulative restriction is compounded if the nipple has a no-go that
is designed to take load. In some older systems, force (load) from above,
for example, during a pressure test against a plug, acts on the no-go
shoulder. To withstand this force, a substantial no-go is needed, resulting
in a significant reduction in ID for each nipple size. Modern nipple sys-
tems have a much smaller step change, since the no-go is designed for
location only.
If a no-go system is limiting size too severely, a selective nipple system
might be used. If selective nipples are used, any number of the same size
seal bores can be run in a completion; in theory at least. Since selective
nipples do not have a no-go shoulder, a different method of locating the
lock in the nipple profile is needed. Most systems require careful manipula-
tion of the setting tool. Some utilize different shaped locking dogs. There
are limitations with selective systems. To reach the lowest nipple in the
string, the lock will have to pass through one or more nipples of the same
size. Because the packing is designed with an interference fit, a degree of
mechanical manipulation or jarring will be required to push the lock past
each nipple. Premature shearing of running tool setting pins is not
uncommon.

3.9 FLOW COUPLINGS AND BLAST JOINTS

Blast joint and flow couplings are short joints of heavyweight tub-
ing. They are usually made from coupling stock, so it is common for the
OD to match the tubing coupling OD, and ID to match the tubing ID.
They are run as part of the completion, and located in places where a
higher than normal rate of erosion is expected.

3.9.1 Flow coupling
Flow couplings are run where there is a large change in diameter, and
where turbulent flow might lead to accelerated erosion. For example, at
the safety valve, cross-overs, side pocket mandrels, and nipple profiles.