Chevron and its partners are underway with conceptual studies for the second subsea development stage for the world-class Greater Gorgon deepwater project offshore Western Australia.

The operator’s Gorgon and Jansz-Io fields in the Carnarvon Basin are well on the way to achieving first gas later this year, but according to Gorgon’s engineering manager, Roger Walpot of Chevron Australia, the company is not hanging around and is already considering the best way of lining up other subsea tiebacks in the vicinity of the ultra-deepwater Jansz-Io field.

Walpot told delegates at the Australasia Oil and Gas event in Perth that there would be at least two new subsea manifolds to be added to the three already installed on the Greater Gorgon fields (two on Gorgon, one on Jansz-Io). ‘Manifold 4’ would see an additional 2-4 wells drilled, while ‘Manifold 5’ would feature another two wells, he said.
On Jansz-Io, additional wells are likely to be drilled in the south-western section of the field, via a drill centre with five wells tying into that, he added. The field itself lies 130 km offshore.

The Greater Gorgon project is of course huge – it’s the largest single gas resource in Australia, with a total resource base of 37 Tcf of discovered hydrocarbons.

Essentially Chevron and its partners will be looking to establish enough tieback prospects for back-filling at a later stage, said Walpot, who was careful not to give out any specific timeline or dates. Slides given during his presentation indicated at least a dozen likely prospects in and around Jansz-Io, which sits in a water depth of around 1,300 m (4,265 ft), and Chevron has previously said up to 30 subsea wells will be drilled on the two fields during their productive lives. The operator has over the past few years confirmed a string of gas discoveries in the Greater Gorgon area, including Satyr, Achilles and Chandon.

Walpot’s colleague David Equid, Gorgon’s upstream facilities project manager, updated delegates on the impressive progress of Greater Gorgon, with the Solitaire vessel currently laying the last section of pipeline this week, and the subsea manifold for Jansz being lowered to the seabed as he gave his own presentation.

Greater Gorgon has 15,000 tonnes in total of subsea structures, with the Jansz structure the heaviest at 900 tonnes. The project’s trees are all identical and weigh in at 80 tonnes each, while some of the spools weigh up to 300 tonnes, he added.

Gorgon and Jansz-Io are tied back to the onshore Barrow Island LNG plant via pipelines and control umbilicals. The Front End Engineering and Design (FEED) and the Engineering, Procurement, Construction Management (EPCM) contracts for the upstream development were awarded to a Technip/JP Kenny 50/50 JV back in 2005.
First deliveries of LNG are expected later this year, with the shallower water Gorgon field to start flowing six months after Jansz-Io.

The Gorgon JV is made up of the Australian subsidiaries of Chevron (operator, 47%), Shell (25%), ExxonMobil (25%), Osaka (1.25%), Tokyo Gas (1%), and Chubu Electric (0.417%).