Page 116 - Well Control for Completions and Interventions

108 Well Control for Completions and Interventions

Figure 3.17 Seal assembly.

When a seal assembly is stabbed into a liner top PBR, a barrier is cre-
ated, isolating the annulus. However, if the tubing above the seal assembly
is not anchored the seal will be dynamic (moving), and less reliable than a
static seal. Most completion engineers will not rely solely on a liner top
seal for well integrity. More usually a production packer (see Section 3.11)
will be set a short distance above the liner top.
Fig. 3.18 shows a WEG, seal assembly, and no-go locator stabbed into
a polished seal bore located above a liner hanger/packer. This configura-
tion provides a continuous conduit from the upper completion and down
into the liner. In the example shown, the production packer is close to
the liner top. This is representative of many completions. While this type
of design is common, it has the disadvantage of creating a trapped annulus
between the packer and the liner top. To overcome this, many comple-
tion engineers require the seal assembly to be nonsealing—a contradiction
in terms. Seals are replaced by wiper rings, or the mandrel is machined
with a spiral groove below the elastomer seals, allowing trapped pressure
to escape. A simple alternative is to drill a hole in the tubing between the
packer and liner top.
The rig site supervisor should be aware of the planned status—sealing
or nonsealing—since it defines the location of critical well barriers. An
unplanned trapped annulus could lead to a tubing collapse.