Is it necessary to install a downhole safety valve in a subsea ... - NTNU

Appendix D
Reliability data dossier
This appendix presents the data dossiers, which form a basis for the input to the reliability
calculations. Reliability data dossiers are databases where the information used in the
calculations are gathered to provide an easy access to the sources. Failure rates are found from
for each component included in the barrier system. The data collected are traceable and
testable for future work based on this thesis. To provide an overview over the leakage
situations of each component the dossiers of this report has included the leakage paths
concerning the ‘TOP’-event, leakage to the surroundings.
Note that the maintenance and test intervals are specific for this report (see subsection 5.4.2
for details).
The schemes are based on data from existing databases. The quality and quantity of the
provided data vary a lot. Many of the different components have got little or no documented
data available. For a wider quantitative study it is suggested that failure rates from several
more sources are supplied and even for the specific area the wells without a DHSV are to be
implemented. A weighing of the different sources according to their relevance for each
individual component is also suggested.
Component: Tubing
Failure rate
(10 -6 /hours)
Reliability data dossier
Failure mode
Data source/comment
0.41 Leakage, TAC Reliability of well completion
equipment - Phase II p.18.
Operational time 13364.03 years,
failures 48.*
Recommended values for calculations:
Failure rate (10 -6 /hrs):
TAC: 0.4
Testing and maintenance:
The tubing is never tested. Repairs on the tubing would require a well workover.
Comments and leakage paths:
The tubing leakage is trough the tubing material or in the tubing connections out to annulus.
The leakage would normally occur in the connections.
* The value does not include installation failures (i.e. failure occurring during the first six days
after installation).
D-1