Thousands of tonnes of climate-damaging methane is leaking each year from abandoned North Sea oil and gas wells, according to new scientific research.
Researchers from the GEOMAR Helmholtz Centre for Ocean Research in Kiel, Germany discovered methane bubbles emerging from the seabed around abandoned wells.
An initial assessment showed that these emissions could be the “dominant source of methane in the North Sea”, they said in the study, published on Friday in the International Journal of Greenhouse Gas Control.
Most of the methane will remain in the water column and will not directly be released into the atmosphere, they said.
The findings prompted the report's authors to call for independent emission measurements so stricter guidelines and legally binding regulations for abandonment procedures can be developed.
The new research used a larger dataset to confirm previous research that looked into the phenomenon in 2012 and 2013 in the central North Sea.
The researchers were able to detect gas leaking at 28 of 43 wells they investigated from 2017 to 2019.
The scientists said the gas originates from shallow gas pockets less than 1000 meters deep below the seafloor that were not the target of original drilling operations.
“We have combined investigations at additional wells with extensive seismic data. The results clearly show that thousands of tons of methane are leaking from old drill holes on the North Sea floor every year,” said report author Christoph Bottner.
Matthias Haeckel, who lead the study, said: “The propensity for such leaks increases the closer the boreholes are located with respect to shallow gas pockets, which are normally uninteresting for commercial use.
"Apparently, however, the disturbance of the overburden sediment by drilling process causes the gas to rise along the borehole.”
The team used available UK seismic data to make further statements about the wellbores in the area.
The study covered an area of 20,000 square kilometres of seafloor — about the size of Wales — containing 1792 wells.
The positions of the boreholes and the location and extent of the gas pockets indicate that this area of the North Sea alone has the potential to emit 900 to 3700 tonnes of methane every year, said Haeckel.
More than 15,000 boreholes have been drilled in the entire North Sea, he pointed out.
Bottner said: "We evaluated a number of factors, such as location, distance to shallow gas pockets, and age, based on our direct measurements and weighted how these factors promote methane gas leakage from old wells.
"The most important factor was indeed the distance of the wells from the gas pockets."
In seawater, methane is usually consumed by microbes, which can lead to local seawater acidification.
In the North Sea, about half of the boreholes are at such shallow-water depths that part of the emitted methane can escape into the atmosphere.
Methane is the second-most important greenhouse gas after carbon dioxide.
The authors of the study have now called on the industry to publish its data and want to see more independent emission measurements from abandoned wells in order to develop stricter guidelines and legally binding regulations for abandonment procedures.
“The sources and sinks of methane, the second most important greenhouse gas after carbon dioxide, are still subject to large uncertainties. This also applies to emissions from the fossil energy sector.
"In order to better understand the reasons for the continuously increasing methane concentrations in the atmosphere and to be able to take mitigation measures, it is important to have a reliable numbers of the individual anthropogenic contributions,” said Haeckel.