Subsea compression in frame for Åsgard

The Åsgard field partnership, led by Statoil, have opted for subsea gas compression to help recover remaining reserves.

Offshore staff

STAVANGER, Norway -- The Åsgard field partnership, led by Statoil, have opted for subsea gas compression to help recover remaining reserves.

Statoil also has assessed potential for subsea gas compression elsewhere on the Norwegian shelf on the Gullfaks field and for the Ormen Lange field, with operator Shell.

“Compressing gas on subsea installations represents a considerable technological leap for the industry,” said Margareth Øvrum, Statoil’s executive VP for Technology & New Energy. “With this technology in place, the recovery factor and producing life can be substantially increased for a number of gas fields.”

At Åsgard, the focus has been on the Midgard and Mikkel gas deposits tied back to the Åsgard B floating platform. Both reservoirs have been developed with seabed installations, exporting their well streams 40-50 km (25-31 mi) via pipelines. For both fields, pressure decline will impact flow to the B platform towards end-2014.

“Installing compressors will sustain the gas flow and ensure a long producing life for the platform,” said Ståle Tungesvik, head of reserves and business development in Statoil. “This makes it possible to recover large volumes – we’re adding 28 bcm (989 bcf) of gas and 14 MMbbl of condensate after a possible investment decision.”

The alternative is to build a new platform with conventional surface compressors. A final decision is due early next year.

However, assessments to date suggest compression is the best commercial option, according to Øvrum. “Moving compression to the seabed gives both improved energy efficiency and lower costs compared with keeping it on a platform or on land. The closer to the well we compress the gas, the higher the efficiency, and the production rates.”

The proposed compression unit comprises a gas cooler, liquid separator, and compressor, the latter likely powered from the Åsgard A oil production ship. Electricity will be converted to mechanical energy by a motor driving the compressor, which consists of numerous vanes around a shaft.

Placing compressors between the reservoir and the host platform should reduce the pressure where the wellstream enters the seabed unit. This should boost production by enhancing the pressure difference between the reservoir and the seabed receiving installation.

Statoil’s partners at Åsgard are Petoro, Eni Norge, Total E&P Norge, and Mobil Development Norway.


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