Statoil is unable to say when subsea compression will start again at the Gullfaks (SEN, 32/15) Field after it was taken offline following a chemical leak on an umbilical line.

Amidst much fanfare, Statoil and its partners Petoro and OMV started the world’s first wet gas compression on the seabed of the North Sea Gullfaks Field in October last year with the aim of increasing recovery by 22 MMboe and extending plateau production by about two years from the Gullfaks South Brent reservoir.

But just a month later it was taken offline because of the chemical leak. The two subsea compressors have been returned to the OneSubsea base at Horsøy where they were manufactured, although they are not faulty.

Statoil spokesman Morten Eek told SEN, “We became aware of a leak from the barrier fluid system connecting back by a 16-km umbilical to the Gullfaks C platform. A chemical fluid has leaked out at some point.”

He said the problem was first picked up at the beginning of November last year when the increased consumption of fluids was noticed.

An investigation group was then set up to try to get to the root of the problem although it has still not been identified.

Eek added, “We removed the two compressors from the system to make sure they were kept apart from the investigation. The leak has nothing to do with the compressors. We can’t say how long it will take until we can put the compressors back into operation.”

Jon Arve Svaeren, OneSubsea’s vice president sales processing systems, added: “The compressors have been removed because they can’t remain there without any support from the umbilical. They will not be returned until the issue has been dealt with and we don’t know when that will be. The compressors have already proved their worth though.”

Leaks connected with subsea systems are nothing new, with both Troll Pilot and Tordis subsea separation and boosting being hit by leaks that were not connected with the main subsea equipment.

The protective structure and compressor station for Gullfaks were installed in early May by the heavylift vessel Oleg Strashnov. On 26 June the compressor and cooling modules were lowered into place from the Seven Viking.

The overall Gullfaks system consists of a 420-tonne protective structure, a compressor station with two 5-MW wet gas compressors totalling 650 tonnes, and all equipment needed for power supply and system control on the platform.

The system can handle a flow rate of 10 MMcm/d and is connected to existing subsea templates and piping 15 km from Gullfaks C.

From the compressor station a power and umbilical cable are tied back to the platform.

The OneSubsea Multiphase Compressor being used on the project is the world’s first subsea wet gas compressor with no requirements for an upstream separation facility or an anti-surge system, which greatly simplifies the subsea system requirements.

The compressor is a contra-rotating machine specifically designed for pressure boosting of unprocessed wellstream.

The multiphase compressor is capable of handling high liquid contents without mechanical issues, with gas volume fractions typically in the range of 95% to 100%.

Offshore