OilVoice - Gjøa Gets Its Sea Legs

Gjøa Gets Its Sea Legs

Tuesday, December 29, 2009

During the last few days the deck and hull of the Gjøa platform have been mated together in the fjord outside the Norwegian town of Stord. There were exacting requirements for precision and weather conditions during the operation, which was a success.

The four-legged hull rose from the sea in the sea off Stord and 'spiked' the deck of the new North Sea giant, Gjøa. Four guide pins had to meet their respective slots in a deck the size of a football field, with a tolerance of just 25 millimetres (1 inch) in all directions.

The guide pins are designed to take the load should the platform list, so that it can be towed to shore before the deck is welded to the hull, allowing mechanical testing and commissioning of the platform to start sooner.

Carried by special barge
During the night, the ballast tanks in the hull were filled with water in order to submerge the structure to a depth of 35 metres. Only five metres of the hull protruded from the water when the barge carrying the platform deck was towed from the quay. The barge carrying the platform deck was manoeuvred into place between the columns of the hull.

Lifting the deck
Slowly but surely, the ballast water was discharged; the hull rose towards the deck and they were mated into one. When the operation was completed, the draught of the hull was 13 metres. The mated platform was then towed to the quay, so that the work of mechanical completion could continue.

Planning saved time
'I am impressed by this operation. It was well-planned, safe and efficient and carried out with the utmost precision,' says Kjetel Rokseth Digre, project manager for Gjøa.

The mating was carried out by Aker Stord, who are constructing the platform for Statoil.

During the past couple of months, more than 2,000 people have worked continuous shifts on Gjøa in order to make it ready for towing to the field in April. By carrying out the mating between Christmas and New Year when most workers are on vacation, a large number of inoperative staff onshore has been avoided.

Building for a new operator
'It was extremely important for us to get this done now. We now have a complete platform structure to work on, and we are doing everything in our power to get Gjøa ready by the agreed date,' says Digre.

Statoil is operator during the development phase of the Gjøa field. The plan is for the platform and the field to be handed over in October 2010, to GDF Suez E&P Norge AS, who will be operator during the production phase. Gjøa will be that GDF Suez's first operatorship for a field in operation.

Key facts
• Currently the largest development project in the North Sea
• The Gjøa oil and gas field covers blocks 35/9 and 36/7 in the northern part of the North Sea, and will be the first development in this area
• It is being developed using a mobile, semi-submersible production platform and five seabed templates.
• The platform will be supplied with power from ashore. Current calculations show that Statoil will avoid emitting 210,000 tonnes of carbon every year
• Estimated recoverable reserves amount to 82 million barrels of oil and condensate, and 40 billion cubic metres of gas. In addition to the above, the Vega satellite field has estimated reserves of 26 million barrels of condensate and 18 billion cubic metres of gas
• The gas will be sent through the Flags pipeline to Scotland while the oil will be piped to Statoil's refinery at Mongstad.
• Licencees to the Gjøa field: Statoil, development operator (20%), GDF Suez E&P Norge AS, production operator (30%), Petoro (30%), Shell (12%) and RWE Dea (8%)

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