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?
Table 3-2 Safety integrity levels for safety functions operating on demand or in a continuous demand mode
from IEC 61508-1, Table 2 and 3)[28]
Safety
Integrity
Level (SIL)
Demand Mode of Operation
(average probability of failure to
perform its design function on
demand –PFD)
Continuous / High Demand
Mode of Operation
(probability of a dangerous
failure per hour)
4 ≥ 10 -5 to < 10 -4 ≥ 10 -9 to < 10 -8
3 ≥ 10 -4 to < 10 -3 ≥ 10 -8 to < 10 -7
2 ≥ 10 -3 to < 10 -2 ≥ 10 -7 to < 10 -6
1 ≥ 10 -2 to < 10 -1 ≥ 10 -6 to < 10 -5
An extract of the minimum SIL requirements given in ref. [28] relating to the object of this
thesis is presented in Table 3-3. The SIL requirement concerning the shut-in of the flow in a
well (Wing valve, Master valve and DHSV) is set to 3. It is therefore reasonable to also require
a SIL3 for a well without a DHSV.
Table 3-3 Minimum SIL requirements - global safety functions, an extract [28]
Safety function SIL Functional boundaries for given SIL
requirement / comments
Isolation of well;
(shut in of one well)
3 The SIL requirement applies to the sub-function
needed for isolation of one well, i.e:
- ESD-node (wellhead control panel)
- Wing valve (WV) and master valve (MV)
including solenoide(s) and actuators
- Downhole safety valve (DHSV) including
solenoide(s) and actuator
Diploma thesis, NTNU 2002
Ref.
APP. A
A.6
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