An international law expert has warned abandoning oil and gas infrastructure in Bass Strait would breach Australia’s obligations under international law, if ExxonMobil pursues this plan in decommissioning its Gippsland offshore project.
Prof Donald Rothwell, who specialises in international law at the Australian National University, said Bass Strait was used for international navigation and had special status under the UN convention on the law of the sea (Unclos) and related International Maritime Organisation (IMO) guidelines.
As a party to the convention, Australia was obliged to remove all structures from Bass Strait when they were no longer in use, he said.
Unclos and related IMO guidelines were “unambiguously clear”, Rothwell said: structures in an international strait within Australia’s exclusive economic zone couldn’t be left “in situ”. “There’s actually an obligation to remove those structures,” he said.
When decommissioning its 50-year-old fossil fuel infrastructure in the Gippsland basin, located up to 77 km off Victoria’s Gippsland coast, ExxonMobil proposed to leave steel structures below depths of 55m “in place on the seabed”.
In a September update, the company said lower sections of steel structures in deep water would remain, with removal “part of a future decommissioning campaign, unless an alternative end state is proposed and accepted by the regulator”.
The National Offshore Petroleum Safety and Environmental Management Authority (Nopsema, the environment, health and safety regulator for offshore facilities) said full removal was “the base case for decommissioning” unless it was satisfied that environmental risks and impacts could be reduced “to as low as reasonably practicable and an acceptable level” in an accepted environment plan.
ExxonMobil plans to submit its plan in early 2025.
Separate approval would be required from the federal environment department under the Environment Protection (Sea Dumping) Act to abandon any infrastructure on the seabed.
“This is a novel issue that hasn’t arisen legally in Australia before,” Rothwell said. He added that the government was well aware of the importance of the UN convention, as well as Australia’s rights and obligations.
“We’re in this interesting position at the moment where the prime minister, the defence minister and the foreign minister constantly reference the law of the sea convention in many different settings, mostly in the context of disputations in the South China Sea and the freedom of navigation.”
He said the situation raised questions about whether the government would uphold its own obligations under the convention in relation to the offshore oil and gas industry.
The Wilderness Society sought Rothwell’s legal opinion after ExxonMobil publicly stated its intention to resubmit plans to leave steel structures in the ocean to Nopsema and the federal environment department.
The Wilderness Society campaigner Fern Cadman said Rothwell’s advice demonstrated a clear requirement under international law for the government and its offshore regulator to insist on full removal.
“Nopsema needs to crack the whip on ExxonMobil to avoid a scenario where the company no longer has financial capacity for clean up and taxpayers are left meeting Australia’s legal requirement and footing the bill,” Cadman said.
Over the next 30 years as projects reach their end of life, an estimated 5.7m tonnes of material – equivalent to 110 Sydney Harbour bridges – needs to be removed from Australian offshore oil and gas facilities, according to the Centre of Decommissioning Australia.
As Australia’s first major offshore oil and gas development, the Gippsland basin was among the first and largest to face decommissioning.
ExxonMobil’s wholly owned subsidiary Esso Australia operated and managed the Bass Strait assets in the Gippsland basin on behalf of the company’s joint ventures with Woodside Energy and Mitsui E&P Australia.
A company spokesperson said it was “progressively decommissioning” its Gippsland basin facilities, including plugging and abandoning more than 120 wells, and contracting a vessel to begin removing topsides and upper jacket sections to 55m deep in 2027-28.
“Esso is currently evaluating a range of decommissioning options including full removal, partial removal and leaving in situ with respect to environmental impacts and risks that may arise, as well as technical, safety and socioeconomic aspects,” the spokesperson said.