In 2017, Woodside commenced decommissioning works at the Enfield oil field, nearby Ningaloo in Western Australia by dismantling and removing facilities associated with the site. In 2018, the Nganhurra floating production, storage and offtake facility (FPSO) was used to flush, isolate and preserve the riser turret mooring (RTM) and subsea infrastructure, before it was disconnected and removed from the field.

As the next step in its decommissioning activities, Woodside initially planned to disconnect, re-ballast to a horizontal position and tow the RTM to Henderson, Western Australia for onshore disposal. However, during preparation activities, the company discovered that one of the RTM’s main ballast compartments could not be re-ballasted to allow for the removal and disposal as planned.

The company assessed other options to decommission the RTM, including repairing and towing, and different scenarios to lift the 2,500 tonne RTM using various specialised vessels for transport to shore. However, it states that these options present significant technical feasibility and safety challenges.

Woodside is now proposing to re-purpose the RTM as a deep-water integrated artificial reef in 150 metres water depth, around 16 kilometres off the North West Cape.

Based on studies and community feedback provided to Recfishwest, integrated artificial reefs can increase fish productivity and environmental resilience, provide an economic stimulus for regional communities, and enhance and provide accessible fishing experiences.

Woodside states that the RTM has been tested for contaminants and contains no Naturally Occurring Radioactive Materials (NORMs) or mercury; an Invasive Marine Species (IMS) inspection found no IMS of concern; and that the RTM contains foam in the top compartment to assist in buoyancy.

Meanwhile, the Australian Conservation Foundation (ACF) says the mooring could contain many tonnes of plastic and manganese, a toxic, soluble heavy metal that could be discharged into the sensitive marine environment around Ningaloo Reef.

Woodside plans to remove as much of the 65 cubic metres of polyurethane foam that is part of the structure as is ‘practicable’, and put grout over the remainder, but conservationists warn this could also end up in the ocean.

Professor Tina Soliman Hunter, Professor of Energy and Resources Law at Macquarie Law School, has advised the ACF that ‘granting permission to scuttle the RTM near Ningaloo to create an artificial reef for recreation purposes, when the removal of the structure is possible, is likely to amount to a breach of Australia’s international law obligations’.

Conservation groups are calling for Woodside to mobilise whichever vessels are necessary to transport the RTM to land. Offshore regulator NOPSEMA is investigating whether Woodside broke the law by letting its equipment fall into disrepair.

Woodside states that it will concurrently seek approval to dispose of the RTM at a deep-water location, should the artificial reef option not be available.