The Statoil solution has been incorporated in the Norne oil production ship and the larger Åsgard A vessel, both located in the Norwegian Sea.

Åsgard A is tied to a subsea field development and a floating gas platform which both rank as the largest of their kind in the world.

This ship is tethered to the seabed by 12 suction pile anchors, with the mooring lines attached to a turret.

The cylindrical turret sits in a 21.6 metre shaft which cuts vertically through the vessel from main deck to hull. 

Wellstreams are carried by flowlines from the subsea templates to flexible risers which pass through guide tubes in the turret and are hung off at deck level.

After passing through chokes to reduce the pressure, the wellstreams are combined in the turret manifold before being divided between two pipes running to the swivel stack – a 14-metre-high unit made of super duplex steel and weighing 125 tonnes. 

This stack is used not only to transmit wellstreams from the turret to the three-stage processing system while the ship rotates, but also to convey gas for injection back into the reservoir to provide pressure support.