An offshore gas well owned by billionaire businessman Kerry Stokes’ Seven Group Holdings conglomerate has been leaking methane into the ocean off the Victorian coastline for more than two years.

The Longtom gas field lies 30 kilometres south-west of the Gippsland town of Marlo. It’s been mothballed since 2015 but is seeping gas from a minor leak detected at one of its shut-in wells and reported to the regulator in 2023.

The Bass Strait’s Longtom gas field, mothballed by Seven Group in 2015, has been leaking methane.

The Bass Strait’s Longtom gas field, mothballed by Seven Group in 2015, has been leaking methane.Credit: Jessica Shapiro

Seven Group, the gas field’s owner, pledged at the time it would fix the leak. However, the National Offshore Petroleum Safety and Environmental Management Authority (NOPSEMA) last week issued a notice saying the company has failed to comply with key commitments it gave in 2023 that required it remediate the leaking well and conduct monitoring of the field.

Fugitive leaks from oil and gas infrastructure, such as wells and pipelines, are major sources of methane emissions that are driving dangerous climate change. Methane is a potent greenhouse gas that warms the planet up to 80 times more than carbon dioxide over two decades, and is responsible for roughly a third of all planetary warming.

The failure of the ASX-listed company, which is 51 per cent owned by the billionaire Stokes family, to conduct monitoring or install mechanical barriers at its leaking well demonstrated an “erosion of good industry practice”, fell short of industry standards and was a potential violation of regulations, NOPSEMA’s notice said.

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The regulator has given Seven Group until March 31 to assess its gas well barrier conditions and stop the leak. It must then reinstate continuous monitoring of the integrity of both gas wells in the Longtom field and submit technical studies to NOPSEMA.

Conservationists said the company’s lack of compliance with its agreed obligations was “not an isolated problem” in the offshore oil and gas industry. Freja Leonard, a campaigner at the Australian Conservation Foundation, called for the regulator to pursue penalties against non-compliant oil and gas producers instead of merely asking them to act more responsibly.

“We urge NOPSEMA to pursue penalties to the extent of the law and regulations to send a clear message that our shared environment isn’t the gas industry’s plaything,” she said.