Page 114 - Well Control for Completions and Interventions

106 Well Control for Completions and Interventions

3.4.2 Liner top packers
Liner top packers can be run as an integral part of the liner system, and
are normally positioned above the hanger slips. They create a seal
between the liner and the supporting casing. There are several reasons
why this may be necessary:
• Isolation of formation pressure below the liner top and from the cas-
ing above.
• Isolation of pressure during stimulation treatment.
• Isolation of formation fluids while cement is setting—prevention of
gas migration.
• Isolation of lost circulation zones.
• Isolation of the production zone in uncemented liner completions.
It is possible to run a liner top packer retrospectively. This would gen-
erally be done where an existing packer failed to set, or had failed an
integrity test.

3.4.3 External casing packers
External casing packers (ECPs) are run with casing or liner. They may
also be called annulus casing packers, or casing annulus packers. ECPs are
run to provide an annular seal between the running string (liner) and the
borehole. They enable multiple zone reservoirs to be completed using
open hole completion techniques (uncemented liner). Communication
devices can be run between ECPs to enable each zone to be produced.
ECPs are run to depth as part of the liner string. Once on depth, an elas-
tomer bag is inflated to provide a seal against the open hole. Inflation is
usually carried out using mud, and/or water. More recently they have
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been inflated using cement.
The ECP is made up of a metal mandrel and collars, an inflation ele-
ment, an inflation valve system, and sealing mechanisms for parts that
move during installation. They are normally identified by the casing OD,
the uninflated seal element OD, and the seal length.

3.4.4 Swell packers
Swell packers use an elastomer seal element bonded to the outside of a
length of pipe. Swell technology uses the swelling properties of different
elastomers that expand to create a seal. Elastomers can be water sensitive,
oil sensitive, or a hybrid that combines both water and oil sensitivity.