Subsea compression online at Aasgard offshore Norway

Offshore staff

STAVANGER, Norway - Statoil says the world’s first subsea gas compression plant has begun operating at the Åsgard production complex in the Norwegian Sea.

Subsea compression should add around 306 MMboe to total output over the field’s life, the operator adds.

Margareth Øvrum, Statoil’s executive vice president for technology, drilling and projects, said: “This subsea technology milestone opens new opportunities in deeper waters, and in areas far from shore.”

Work started on the program in 2005, and the plan for development an operation was approved in 2012. Overall, project costs totalled just above NOK 19 billion ($2.3 billion).

Over time, natural pressure in the reservoir drops, with compression then required to recover more oil and gas and direct these reserves to the platform. The closer to the well that compression takes place, Statoil says, the more oil and gas that can be recovered.

Traditionally, compression plants are located on platforms or onshore, but Åsgard’s plant is the first to operate on the sea floor, in this case in 300 m (984 ft) of water.

The Midgard and Mikkel gas reservoirs, both connected to the Åsgard complex, were originally developed using subsea installations. The two gas compressors now installed on the seabed are both close to the wellheads.

Prior to gas compression, gas and liquids are separated out, and after pressure boosting are recombined and sent through a pipeline 40 km (25 mi) to the Åsgard B platform.

Statoil estimates that subsea compression should boost recovery from the Midgard reservoir from 67% to 87%, while recovery from the Mikkel reservoir should increase from 59% to 84%. Both reservoirs’ productive lives should therefore be extended through 2032.

Statoil says that over the course of the project, over 40 new technologies have been developed and deployed following testing and verification. Some of this work has taken place at the company’s Kårstø laboratory in Western Norway.

Various small and large suppliers helped develop the underwater compressor system.

One critical component of the project, Statoil adds, was establishing support functions onshore. A spare compression train will be stored at the onshore supply base Vestbase in Kristiansund, which will also perform regular maintenance of the subsea modules.

In addition to improving recovery subsea gas compression will be more energy efficient than the traditional topside solution, the company points out, as the technology reduces energy consumption and carbon-dioxide (CO2) emissions over the field’s life.

9/17/2015

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