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Statoil says first ever subsea gas compression plant now online

22 September 2015

Statoil announced on September 17 that the first subsea gas compression facility in the world had started operations at Åsgard in the Norwegian Sea. Subsea compression will add some 306 million barrels of oil equivalent to total output over the field’s life, the Norwegian company said, and offers new opportunities in deeper waters and in areas far from shore.

Åsgard seabed compression facility - Image: Statoil ASA
Åsgard seabed compression facility - Image: Statoil ASA

 “This is one of the most demanding technology projects aimed at improving oil recovery.  We are very proud today that we and our partners and suppliers have realised this project that we started ten years ago,” said Margareth Øvrum, Statoil’s executive vice president for Technology, Drilling and Projects.

Recovery from the Midgard reservoir in Åsgard will increase from 67% to 87%, and from 59% to 84% from the Mikkel reservoir.  Overall, 306 million extra barrels of oil equivalent will be recovered.

The new compressor solution will increase recovery rates at Midgard and Mikkel, but will also extend the reservoirs’ productive lives until 2032.

As a field gets older, the natural pressure in the reservoir drops. In order to recover more oil and gas, and get this to the platform, compression is required. The closer to the well compression takes place, the more oil and gas can be recovered.

Traditionally compression plants are installed on platforms or onshore, but this plant is located in 300 metres of water. Due to the challenging location, quality in all parts of the project was essential, and will help ensure high regularity, maximum recovery and robust production. The project started in 2005, and the plan for development and operation (PDO) was approved in 2012.

An estimated eleven million man-hours have been spent from the start until completion. More than 40 new technologies have been developed and employed after prior testing and verification. Some of this work took place at Statoil’s Kårstø laboratory in Western Norway.

Overall, project costs were just above NOK 19 billion ($2.25 bn). Many small and large suppliers helped develop the sophisticated underwater compressor system.

Establishing the necessary support functions onshore has been an important part of the project. A spare compression train will be stored in custom-designed halls at the Vestbase onshore supply base in Kristiansund. High-quality maintenance  of the subsea modules will be performed there.

The Midgard and Mikkel gas reservoirs were developed using subsea installations. The two gas compressors now installed on the seabed are located close to the wellheads.

Moving the gas compression from the platform to the wellhead substantially increases the recovery rate and life of the fields. Prior to gas compression, gas and liquids are separated out, and after pressure boosting recombined and sent through a pipeline some 40 kilometres to Åsgard B.

In addition to improving recovery subsea, gas compression will be more energy efficient than the traditional topside solution. The technology significantly reduces energy consumption and CO2 emissions over the field’s life.

Today, 50% of the company’s production is recovered through some 500 subsea wells. Statoil’s subsea expertise is essential to successful production efficiency improvement and increased oil recovery efforts, the company says.

“Subsea gas compression is the technology for the future, taking us a big step closer to our ambition of realising a subsea processing plant, referred to as the subsea factory”, Øvrum said.
Such a plant will facilitate remotely controlled hydrocarbon transportation.  Current topside operations will thus be moved to the seabed, allowing oil and gas to be recovered that would not otherwise be profitable.

This is an important element of increased recovery plans on the Norwegian continental shelf.

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