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

Is it necessary to install a downhole safety valve in a subsea oil/gas well?
master production valve and the wing valve are ordered to close in and be tight. Only the static
barrier scenario of the production phase is included.
The barrier diagrams are based on the following assumptions:
The master production valve, wing valve and the DHSV have been given a close
command from the surface control.
The system is shut-in.
Leakage through the tubing and back into the tubing is possible but not considered here.
The x-mas tree is not considered as a single barrier, but each main component is
regarded as a barrier.
The probability of leakage to the surroundings through the casings and cement is very
low and is not accounted for in the barrier- and fault tree analysis.
The leakage paths are illustrated in Figure 5-2. The reliability data dossiers in appendix D
include a column where the applied leakage modes of each valve are listed.
The barrier diagrams for the oil/gas production well with and without a DHSV are presented in
Figure 5-3 and Figure 5-4.
Diploma thesis, NTNU 2002
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