Gas-Lift Valves Barrier Testing
Sven Aarrestad
International Research Institute of Stavanger AS
Jørn Andre Carlsen
StatoilHydro ASA
Abstract
Statoil defined in 2004 the gas-lift valve (GLV) to be a part of the primary barrier envelope. Back check valves in flow control devices are designed and intended to prevent reverse flow. But according to the ISO 17078-2 “they are not designed nor intended to be a part of the safety system, nor to be a part of a tight shut-off pressure safety seal”.
To qualify GLV`s as a barrier element, Statoil issued a test program with emphasis on the sealing properties of the back check valve in the flow control device, close up to the ISO 14310. Testing with gas, no more than 20 ml/10 min is allowed to pass the barrier.
In 2005 Statoil and IRIS (International Research Institute of Stavanger – former Rogaland Research Institute) started testing of GLV`s supplied by Schlumberger, Baker Oil Tools, Weatherford, and later on PTC (2007). The intention was to improve valve design and reliability, and secure the quality during the factory acceptance test (FAT) and the operating sequences in the field.
This was based upon the same philosophy that was used when IRIS tested down hole safety valves for Statoil in the early 1980`s.
None of the valves satisfied the test acceptance criteria stated in Statoil`s qualification program for testing of GLV`s. Based upon the learning from the testing, the industry can now supply valves qualified according to the barrier acceptance criteria. The results will reduce the number of well interventions as:
- Dummy valves in sub sea wells can be replaced by shear open valves.
- GLV`s will not be washed out during the unloading nor during the gas lift sequences.
- The entire barrier envelope will be intact during the entire expected valve lifetime, included several years installation in a side pocket mandrel prior to the operating sequences.