Downhole safety valves can easily become corroded or damaged due to wireline activity. Standard chevron stacks are commonly provided with insert safety valves incapable of effectively sealing in this damage.
This results in a leak path that allows hydrocarbons to migrate up the control line.
The only solution for a leaking safety valve is to perform a straddle or workover, and replace the damaged valve, which is costly and time consuming.
In 2013 TAQA released SwellStack, a swellable sealing solution that can be installed in place of an existing chevron stack, sealing in damage within the bore of a safety valve.