Page 232 - Well Control for Completions and Interventions

226 Well Control for Completions and Interventions

features and depths. The concept of using a well schematic to identify
4
well control barriers is said to have first begun in Norway in 1992. Since
then the use of barrier schematics has gained in popularity and is rapidly
becoming standard practice for many operating companies.
A barrier schematic clearly illustrates both primary and secondary bar-
rier envelopes, as well as listing the barrier elements. The barrier sche-
matic can be used to detail how each barrier is tested. On a long and
complex completion or intervention, the barrier envelope may change
several times as the operation progresses. Embedding a barrier schematic
for each phase of the operation in the work programme or procedures
manual helps well site personnel keep track of well control barriers as the
job progresses. This reduces the risk of errors in barrier identification,
and consequently reduces the possibility of barrier failure. It also improves
response time where barriers do fail, and will help in planning the actions
necessary to reinstate the vital primary barrier.
5
Commercial barrier drawing software is now available, and the draw-
ings produced are similar to those found in NORSOK D 010. The
example barrier drawings shown here are based on the NORSOK model.
By convention, these drawings display the primary barrier in blue, and
the secondary barrier in red.
When preparing barrier drawings, the correct identification of both
primary and secondary barrier envelopes is important. A simple approach
is to ask, between the reservoir and surface, what parts of the wellbore/
completion are exposed to reservoir fluids, i.e., the primary well barrier
envelope. If an element of the primary barrier envelope fails, where is the
fluid going next? Anything exposed to fluid leaking from the failed pri-
mary barrier forms the secondary well barrier.
The next few pages are a series of well barrier drawings for some
commonly performed completion, workover, and intervention
operations.