This paper provides an insight into the challenges encountered and overcome during installation of 20 subsea structures, some close to 1000 t in weight and in water depths of up to 1350 m, for the Gorgon project offshore Western Australia.
Introduction
The Gorgon project development comprises the Gorgon and Jansz-Io gas fields located off Australia’s northwest coast, in water depths of 200 and 1350 m, respectively. Ten structures were installed in 20 separate lifts, using the multipurpose heavy-lift and pipelaying vessel Sapura 3000. Tight angular tolerances and low landing speeds were required to meet the structures’ design criteria.
All structures were loaded onto cargo barges and towed to site for installation. Liftoff and deployment through the splash zone were performed with the Sapura 3000 main crane. Depending on the size of the lift and the installation water depth, the structures were either deployed directly to the seabed using the crane (in the Gorgon field only) or transferred to a deepwater lowering system (DLS). Structure foundations were either skirted mud-mat types (deep water, soft-seabed locations) or suction piles, and were all fitted with fixed guideposts to assist with module-landing operations.
Installation Analysis
Subsea-structure foundations and modules are typically designed with landing-speed limitations; exceeding these might cause overstress within the structures.
