It is widely recognised that the main risk introduced by gas lifting, is associated with potential uncontrolled release of high pressure gas from the tubing / production casing annulus.
Historically a variety of solutions have been deployed to mitigate this:
- Actuated valves on the gas injection lines upstream of the wellhead.
- Check or non return valves (NRV’s) in the wellhead VR profile.
- Downhole annulus safety valves (DH-ASV’s).
It is now widely recognised that these solutions are flawed:
- Falling objects in the wellbay will most likely cause the injection line to break between the actuated valve and the wellhead.
- Actuated valve stem seals are a potential source of leak (single barrier).
- NRV’s in the wellhead are prone to damage due to chattering and erosion.
- DH ASV’s are reputedly unreliable and still expose the platform to a large inventory of gas.
The solution PTC offers, our surface annulus safety ( SAS) valve systems, are actuated NRV’s which are set in the wellhead VR profile. They are differentiated from the existing solutions, in that they address all of the above listed flaws.
As a result, they are now widely accepted as a low cost solution (instead of a workover) in wells with failed DH ASV’s.
They are also increasingly being specified in new gas lifted completions, either as an alternative to or in addition to DH ASV’s, since they demonstrably reduce the risk to a level which is ALARP.
