PERTH, Australia -- Bids are in for work on the subsea tieback of the Jansz field to shore at Barrow Island, said David Equid, Gorgon Upstream, during his presentation at DOT International Asia/Pacific in Perth, Australia.
Jansz is being developed with an initial 10 subsea wells tied back directly to an LNG plant onshore. Pipeline installation is the main challenge, Equid explained.
Early evaluation of the seabed bathymetry at Jansz processed from the 3D seismic identified the presence of major seabed features and irregularities in the proximity of where the proposed Jansz subsea manifolds would be installed, Equid said.
These would complicate not only the placement of the subsea structures and associated components but also routing of the pipelines to tieback the subsea facilities to the LNG plant.
A number of tieback routes were considered including a northern route that would originate in 1,350-m water depth and traverse an underwater scarp with sections inclining up to 70° and with cliff heights up to 100 m.
For this route to be viable, it was proposed that a trench be cut at the scarp shoulder, adjusting the exit angle of the pipeline and effectively reducing the height and length of the resulting span, Equid said.
Subsea compression would be needed later on, Equid added, because of the long distance and steep incline.