INPEX has completed the offshore pre-lay of the 77 kilometre chain and cable mooring system for its Ichthys LNG project located in the Browse basin, off the northern coast of Western Australia, the company announced in mid-May.

As part of the mooring system, 49 chains were laid on the seabed in water depths of up to 250 metres and anchored to foundation piles—5.5 metres in diameter and 63 metres long.

The mooring system will secure the project’s two offshore facilities; the central processing facility (CPF) and floating production, storage and offloading (FPSO) facility, located in the Ichthys field seabed for at least 40 years of continuous operation.

Once located in the field, the CPF will deliver natural gas and some condensate through an 890 kilometre subsea gas export pipeline to onshore processing facilities in the Northern Territory.

Most condensate will be processed through the FPSO and shipped directly to market from the field, INPEX said.

More than 40,000 tonnes of large-scale anchor chains were built over nearly 18 months for the project by teams around the world, with each chain link weighing more than 700 kilograms.

INPEX said the 28 CPF mooring chains required more than 25,000 tonnes of mainly 178 millimetre diameter chain, while the 21 FPSO mooring chains needed more than 15,000 tonnes of mainly 161 millimetre diameter chain.

Ichthys project managing director Louis Bon said the mooring system pre-lay was a significant undertaking with challenging soil conditions for the piling scope of work.

“Despite the difficulty of the task, I’m proud to say that it was successfully completed without a single lost time injury or any harm to the environment,” Mr Bon said.

“For example, because the Ichthys field is located just 120 kilometres from the main humpback whale migratory routes and calving grounds of North West Australia, an early decision was made to avoid pile driving during the whale calving period where associated underwater noise may have created a disturbance.”

Mr Bon said the successful completion of the mooring chains pre-lay marked another major step ahead of the arrival of the CPF and FPSO currently under construction in ship yards in South Korea and, once completed, will be towed 5600 kilometres to the Ichthys field.

“The offshore facilities will operate for decades and the mooring system plays a key role in ensuring their integrity.”

In addition to the mooring system, more than 16,000 tonnes of subsea structures and 140 kilometres of rigid flowlines have been installed across the Ichthys field to efficiently extract gas and condensate.