Page 230 - Well Control for Completions and Interventions

224 Well Control for Completions and Interventions

In the event of primary and secondary failure, and where no wire cut-
ting BOP is fitted, it may become necessary to cut the wire with the tree
valves. If the tree valves are not designed to cut wire, the gate may be
damaged and it may not be possible to obtain a seal with the valve closed.
If a tree valve must be used to secure the well, always use the upper mas-
ter valve.
• If the lower master valve is damaged, two mechanical set barriers must
be installed in the wellbore before repairs can be made.
• If the swab valve is damaged, it would not be possible to flow the
well whilst maintaining double barrier isolation (swab valve and
swab cap).

6.7.2 Coiled tubing
6.7.2.1 External pressure control
Primary Barrier.
• Stripper rubbers and riser.
• Christmas tree valves when deploying tools in and out of the riser. If a
downhole lubricator valve is fitted, this would be the primary barrier
when installing tools into or out of the well.
• Gate valves if a tool-string deployment system is being used.
Secondary Barriers.
• BOP rams.
• SCSSSV or lubricator valve if the coil tubing BHA is above.
Tertiary Barrier.
• Shear and seal capability in BOP. For many operations, a shear/seal
combination BOP will be mounted immediately above the tree.
• Some trees are fitted with gate valves able to shear coil tubing.

6.7.2.2 Internal pressure control
Primary Barrier.
• Check valves (nonreturn valves) in the BHA.
Secondary Barriers.
• Fluid pumped into the coil to prevent hydrocarbon ingress and valves
on the side of the reel.
Tertiary Barrier.
• Shear and seal capability in BOP. For many operations a shear/seal
combination BOP will be mounted immediately above the tree.
• Some trees have been fitted with gate valves able to shear coil tubing.