Significant corrosion and leaking have been detected in a number of coal seam gas wells in Queensland, with experts now concerned about the broader implications for groundwater contamination.
The reports released under right-to-information laws have also raised questions about the role bacteria may be playing in the breakdown of gas well casings.
One major industry service provider is now marketing "expandable patches" to address the "systemic" problem.
Some of the gas wells found to be leaking were less than 20 years old, and RMIT University's Gavin Mudd raised concerns about the possible long-term impact of the gas industry.
"There is real concern about what happens in 50 years' time or longer," Dr Mudd, an associate professor of environmental engineering who has examined the documents, said.
"Cement doesn't last forever, especially when you've got either salinity or salt … salt can affect the integrity of cement."
Environmental group Lock the Gate has obtained reports and correspondence between Queensland regulators and gas companies regarding the remediation of a number of corroded and leaking gas wells.
In one report, a gas company stated "compromised cement" was found to be "allowing aquifer contact with the casing".
"The most significant defect indicates 65 per cent wall [well casing] loss," the report said.
The documents referenced gas wells located across the Surat Basin, a geological zone that starts about three hours' drive west of Brisbane and stretches into central Queensland.
The reports are from between 2020 and 2021 and show that the corrosion issues with the CSG wells were overseen by state compliance regulators and resolved by the gas companies.
Bacteria an 'unusual problem'
Saltel Industries is a major international service provider for the petroleum industry specialising in "remedial" products and services. It markets a number of "patches" to assist gas companies to repair corroded casings.
In a 2019 press release, the company said it was approached by "one of Australia's leading natural gas producers to address an unusual problem" with the corrosion of gas wells "suspected to be caused by bacteria growing under specific pressure and temperature environments".
In the press release, Saltel Industries also said "corrosion damage can leave less than 80 per cent of the [gas well] casing metal thickness".
Dr Mudd said there was a range of processes that bacteria could be involved in that could lead to corrosion risk.
"If you've got bacteria consuming carbon, for example, that can release carbon dioxide, which in groundwater then forms carbonic acid, which can cause corrosion," he said.
"We know this from many decades of experience with groundwater bores, petroleum bores, and even geotechnical engineering projects of tunnelling."
CSG wells are drilled hundreds of metres underground into coal seams and are constructed from steel casing and sealed with cement.
Dr Mudd said the right-to-information documents revealed there were issues with CSG well integrity, which had the potential to impact groundwater.
"It may mean that you've opened up pathways for a potential cross-contamination of groundwater," he said.
"There is always these concerns around how long can we maintain well integrity … that's certainly an open question and I don't think that has really been resolved."
A spokesperson from the state regulator, Resources Safety and Health Queensland (RSHQ), said it audited and inspected operators and that management of [gas] well integrity and bacterial management were covered by current legislation.
"RSHQ will continue to work with operators to address risks that may cause harm to resources workers," the spokesperson said.
"Since 2020, less than 1 per cent of Queensland’s wells have reported integrity issues."
Under Queensland legislation, there are mandatory compliance reporting requirements but as per the code of practice, "it is the responsibility of the operator to ensure that these reporting requirements are met".
Farmer says 'it's not worth the risk'
Dalby farmer Russell Bennie has a decommissioned CSG well on his farm, but he claims the area has never been adequately remediated.
"I've had to deal with subsidence and pit holes, because in those days they were digging pits into the ground to hang onto the drilling mud," he said.
Mr Bennie said there were still patches of gravel in his paddock that were brought in when the well was drilled.
"The gravel acts as a dam wall and backs water up, and it prevents me from accessing the track I need to use to farm," he said.
Mr Bennie claimed his attempts to have the responsible gas company address the issues had been unsuccessful, and follow-up from state regulators had been inadequate.
He was worried about the long-term impact of the gas industry on the designated strategic cropping land that he farmed.
"It's not worth the risk, even if there's only a 5 per cent risk of adding an adverse outcome," he said.
Regular inspections and maintenance
Matthew Paull, the Queensland director of the Australian Petroleum Production and Exploration Association (APPEA), said the gas industry took environmental protection seriously.
"All companies undertake regular inspections and maintenance of infrastructure and make financial provision for decommissioning and rehabilitation — companies are legally required to fund these activities themselves," he said.
Mr Paull said a new Financial Provisioning Scheme established in 2018 further bolstered "comprehensive" state legislation.
"The scheme is essentially an insurance policy for government with companies contributing each year to a pooled fund that, as a last resort, government can use to fund rehabilitation," he said.
'Unknown leaks'
In another report, revealed through Right to Information laws, a CSG well had been found to have an "unknown leak" and a "failed casing pressure test".
Dr Mudd said the leaks could also mean that methane gas might have been leaking uncontrollably through the ground and around the wellhead, which was both a safety risk and harmful to the environment.
"The question that I suppose we can't answer from the information available is how representative those bores [CSG wells] are of the rest of the tens of thousands of bores that exist across Queensland," he said.
CSG development continues to grow in Queensland.
In the Surat Basin, there are already 8,600 gas wells and it's forecast to grow to around 22,000 gas wells in the coming decades.
"Ultimately … we need really good surveillance of all the bores, and to make sure that they're in good condition and working well," Dr Mudd said.
Plugged and abandoned
In Queensland, regulation of CSG wells both during and after production is managed under the Petroleum and Gas (Production and Safety) Act 2004. There is also an accompanying code of practice.
A fact sheet about decommissioning coal seam gas wells has been published by Gas Industry Social and Environmental Research Alliance (GISERA), a collaboration between CSIRO, state and federal governments, and industry.
When a CSG well is decommissioned, the wellhead is removed, the casing is cut off "at least 1.5 metres below surface" and the well is then plugged with cement.
