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World's first subsea compression online

Written by  Thursday, 17 September 2015 03:27

At 300m below the surface of the Norwegian Sea, the world’s first subsea gas compression facility has come on stream, Statoil announced this morning. 

The NOK 19 billion (US$2.34 billion) Åsgard subsea gas compression project, known as project Nemo to some internally, is seen as a major step towards Statoil’s subsea factory vision, which would enable a complete suite of processing technologies on the seafloor, thereby creating new possibilities to extract hydrocarbons in deeper, harsher waters, further from shore. 

Alongside Åsgard, which uses technology developed by Aker Solutions, Statoil is also developing the Gullfaks subsea wet gas compressor facility, a smaller facility, but also a first, as it will not require separation, and which was installed in July and uses a OneSubsea system. It is due to be tied back to Gullfaks C in later summer-autumn. 

“We are very proud today that we together with our partners and suppliers have realized this project that we started 10 years ago,” says Margareth Øvrum, Statoil’s executive vice president for Technology, Drilling and Projects. “Subsea gas compression is the technology for the future, taking us a big step closer to our ambition of realizing a subsea processing plant, referred to as the subsea factory.”

Subsea compression helps maintain reservoir pressure and increase recovery rates. Traditionally, compressors are located on platforms, but, the closer to the reservoir the compression takes places, the more hydrocarbons can be recovered. 

At Åsgard, introducing subsea compression will add some 306 MMboe to total output over the subsea Midgard and Mikkel reservoirs’ lives, which will be extended out to 2032. Moving the compressors to the seafloor also reduces the need for extra equipment topsides, is more energy efficient and reduces CO2 emissions, says Statoil.

The project involves two 10MW gas compressors, a scrubber, pump and coolers, electrically powered from the Åsgard A floating oil production vessel. The compressor station is measures 75m x 45m x 20m and weighs 4800-tonne with a 21cu m/d (gas) capacity. 

The idea for subsea gas compression dates back to 1985, when now Aker Solutions first chief engineer Kjell Olav Stinessen was working at Norway’s Kvaerner. Aker Solutions started working with Statoil on the concept in 2005 and was awarded a contract to deploy the technology on Åsgard in 2010. 

At Åsgard, prior to gas compression, gas and liquids are separated out, and after pressure boosting recombined and sent through a pipeline some 40km to the Åsgard B semisubmersible gas production platform.

Statoil says some 11 million man-hours have been spent on the Åsgard project, and more than 40 new technologies have been developed and employed. 

To ensure continuity, should one of the compressors fail, a spare compression train is being stored in custom-designed halls at the onshore supply base Vestbase in Kristiansund.

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