A study of one abandoned coal exploration borehole in a Queensland paddock has found it was leaking the same amount of greenhouse gases in a year as about 10,000 cars – and there could be thousands more just like it.
Scientists at the University of Queensland also monitored a second coal exploration bore that was emitting about the same amount of methane and was forcing groundwater several metres into the air like a geyser.
The federal government has previously published estimates that there are about 130,000 coal exploration bores across the state in the Surat and Bowen coal basins.
Sign up: AU Breaking News email
The discovery raises the possibility of major and unreported emissions of the greenhouse gas that, per kilogram, warms the planet 80 times more than carbon dioxide over a 20-year period.
Climate experts say because of its short-term potency, controlling methane could be a quick route to slowing down global heating in the coming decades.
UQ scientists monitored one borehole in the paddock in the Surat basin for seven days using special methane-detecting camera equipment.
The hole – about 100 metres deep – was not visible from the surface and had been previously covered by dirt, but researchers were tipped off by a gas company doing survey work in the area. There was also no grass growing in a patch surrounding the hole.
The camera detected methane being released at an equivalent annual rate of 19,768 tonnes of CO2, if using a calculation of methane’s impact over 20 years. This was the same as 10,000 cars each driving 12,000 kilometres a year.
Associate Prof Phil Hayes, a co-author of the research published in the journal Science of the Total Environment, said the borehole had been there for about two decades but it wasn’t possible to say for how long it had been leaking methane or at what rate.
The rate of leaking could be influenced by the geology beneath and by the state of water extraction in other areas that can change the pressure of the groundwater, he said.
A second and older Surat basin borehole that did not feature in the research was also monitored that would “erupt with water every 10 minutes because of the gas pressure building up beneath it”, Hayes said.
He said the hole had since been sealed but at the time of the monitoring it was emitting at a similar rate to the first borehole.
Hayes, of the university’s Gas & Energy Transition Research Centre, said the modern standard for decommissioning exploratory bores was to fill them with concrete.
LoopUQ Gas & Energy Transition Research Centre equipment detecting methane.
The study said other boreholes completed by the “same combination of drilling contractor and coal company”, which were not named, were found to have a “bag of cement placed over the open hole near [the] surface before replacement of soil.”
Hayes said: “These boreholes are drilled by coal exploration companies. They can be done in one day and they tell the company about the quality of the coal or how it changes from one area to the next.”
While there were an estimated 130,000 coal boreholes in Queensland, Hayes said he thought only a fraction were likely leaking.
“What we have uncovered is a further source of methane that needs to be taken into account in our greenhouse accounts but it’s something that is easy for us to manage,” he said.
“It requires some action by the government and exploration companies to identify and then plug these holes. If we’re trying to work on climate change in the next decade, then we would do well to focus on methane as well as carbon dioxide.”
A spokesperson for the Queensland government’s natural resources and mines department said the state’s regulations “require petroleum and coal companies to plug, cap and fully remediate any boreholes and wells they abandon to prevent legacy boreholes and fugitive gas emissions”.
“The issue of historic legacy coal exploration boreholes is more complex. These would have been drilled and abandoned prior to government introducing more stringent and detailed borehole drilling and abandonment requirements.
“In many cases, these old boreholes may not have been properly mapped and the resource company that drilled and abandoned them no longer exists.
“When the department becomes aware of a significant community health and safety risk associated with a legacy coal borehole, it is assessed to determine whether remediation is required.”
The Guardian contacted the Queensland Resources Council for comment.
