Page 223 - Well Control for Completions and Interventions

CHAPTER SIX

Well Barriers

Well barriers are fundamental to well integrity and well control. An
uncontrolled blowout can only occur if more than one barrier fails.
Understanding the physical properties of a barrier, where the barriers are
located, how they are tested, and the actions to take if a barrier fails, are
critical skills for anyone working in completions or interventions. During
interventions and workovers, barrier elements and the barrier envelope
often change as the job progresses. Those working in completions and
interventions must be able to clearly identify each change of barrier ele-
ment, and how the barrier envelope changes throughout the operation.
Many operating companies now incorporate barrier diagrams in work
programmes. These diagrams clearly identify the primary and secondary
barrier envelopes, all the individual barrier elements, and how they
should be tested. Any change to the barrier configuration requires a new
barrier diagram. This is an excellent system, and if properly implemented
will mean those tasked with carrying out the work are always clear about
where barriers are, how they change as work progresses, and crucially,
how to respond to a barrier failure.

6.1 DEFINING WELL BARRIERS AND WELL BARRIER
ELEMENTS

The Norwegian regulatory authority NORSOK define a well bar-
rier as an “envelope of one or several dependent barrier elements pre-
a
venting fluids or gases from flowing unintentionally from the formation,
into another formation or to surface.” They further define a well barrier
element as an “object that alone cannot prevent flow from one side to
1
the other side of itself” (sic). This is an important distinction, and not
always made in some well control manuals and text books.

a
A pedantic point. This should probably read liquids or gases. Gas is a fluid.
Well Control for Completions and Interventions. © 2018 Elsevier Ltd.
DOI: https://doi.org/10.1016/B978-0-08-100196-7.00006-3 All rights reserved. 217