Summary
Degradations or interruptions of the original well-barrier elements might
occur at offshore wells after some time in operation. Experience from the
Norwegian Continental Shelf (NCS) has shown that these problems are not always
treated as thoroughly as expected by the parties involved. This paper presents
an approach for an efficient visualization and description of interrupted well
barriers, basically to increase the well-barrier control and management. By
mapping the history of operational demands and load picture of the well in
combination with the status of well barriers, a consistent basis for
evaluations is obtained. The main intention is thus to realize the real well
problem and its underlying causes in a controlled and systematic manner. Then,
the responsible parties involved can take action more accurately according to
the type of failure that has been revealed.
Introduction
Interrupted barrier elements are related to well integrity and are critical
from the point of view of safety, but also concerning production regularity and
costs. Failure in the well-barrier functions caused by degradations or
interruptions of barrier elements needs immediate attention from the
responsible bodies. During drilling and well activities, there are always to be
at least two independent and tested well barriers after the surface casing is
in place, according to the activities regulations of the Norwegian Petroleum
Safety Authority (PSA) (2006).
Experience from PSA (Vignes et al. 2006) has shown that barrier failures
occur both in newly drilled wells and in wells that have been in operation for
some time. Well-integrity failures may be latent in the early constructing
phase, or imposed through later maintenance tasks. Shifting between well
operational phases can also initiate abnormal load situations causing
well-integrity failures to occur. Many of these "unexpected" loads are
not necessarily taken into account in the design phase. An investigation
carried out by the PSA on the NCS showed that 14% of 309 checked wells
currently in operation had problems with, or deviations related to, the well
integrity (Vignes et al. 2006). Experience has also shown that integrity
problems are not always treated as systematically and thoroughly as expected by
the well operators.
The main objective of this paper is to present a visualization method for
the purpose of evaluating well-integrity problems that communicates facts about
integrity problems to the responsible bodies. Intended users of the approach
are operators, contractors, government/safety authorities, researchers, and
consultants who have interest in carrying out assessments of well-integrity
matters. As one possible application, the options regarding the future
operation of wells may be clarified by the operator, with new preconditions and
operational limitations.
A brief introduction to the technical-problem area is given from a system
perspective. Important casing-hanger loads are described including those
operational and geological factors that make the casing-hanger load reach
abnormal values. Then, a description of the three-step visualization method
follows. Implications of the method are discussed, and some remarks regarding
applications are given. Finally, some conclusions are outlined.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
9 January 2007
- Meeting paper published:
5 March 2007
- Revised manuscript received:
23 May 2008
- Manuscript approved:
2 June 2008
- Published online:
1 June 2009
- Version of record:
1 June 2009
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