The lower section or “legs” of an offshore platform. Platform underside structure fixed to the seabed using piles. These piles must be able to resist tension as the hydrodynamic forces on the structure have a tendency to cause overturning.

Jacket and topside make the lower and upper parts of the platform.

Platform installation
Jackets and topside decks need to be transported to the well location. The vessels sail to the location with the topsides or jacket on board, and accurate positioning on DP takes place on location in the same way as for removals. The active motion compensation system takes out all motions of the topsides relative to the base structure before lowering the topsides onto the base structure without impact.

Once the jacket is in its final position and piled, the deck is lifted into position and welded to the jacket. Following the installation, the hook-up is completed to services and production lines on the jacket. Any additional modules are lifted into position, fixed and hooked-up to the deck unit, before the platform is commissioned.

Platform installation is executed with the same equipment on the vessel: topsides are installed with the topsides lift system (TLS), jackets with the jacket lift system (JLS) or, in case of small jackets, with a tub-mounted crane.