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Research on the amount of gas leaked from onshore oil and gas wells raises "serious questions" over the development of fracking in the UK, Greenpeace has said.

Around a third of former onshore oil and gas wells are leaking methane gas, according to the research led by scientists at the University of Durham.

But it found the leaks produced less methane than agricultural use.

The industry body said the findings should reassure people.

"What ReFINE has shown is that the public should have no health or environmental concerns about emissions from properly decommissioned wells adhering to current industry standards."

"Indeed the research has found that in the minority of cases where they have recorded some methane emissions from decommissioned wells, these emissions are typically less than one would get from just a handful of livestock grazing in the same fields," said Ken Cronin, Chief Executive of UKOOG, the representative body of the UK Onshore Oil & Gas industry.

Around 2000 onshore oil and gas wells have been drilled in the UK.

Fracking for shale oil and gas could result in many more.

Doug Parr, Chief Scientist at Greenpeace, says that's a worry given the levels of methane leakage uncovered in the study.

"If even an industry-funded study suggests that 30% of conventional wells appear to be leaking, it raises serious questions over the long-term impact of the extensive development of unconventional gas in the UK which is clearly the government's plan," he said.

Methane Leakage

The study sought to clarify how many former or decommissioned wells might be leaking methane.

Tests were carried out at wells ranging from 8 to 79-years-old.

Levels of the gas were tested at 102 locations which had previously been working oil or gas sites.

The sites had all been decommissioned, which involves the wells being cut-off, sealed and buried to a depth of 2 metres.

In the majority of cases, the methane levels were either lower than or comparable with that in nearby fields.

But at 31 sites methane levels found at the soil surface were significantly higher than those found in control samples taken nearby.

"The point is that even with proper decommissioning you will still have those wells that leak as cement cracks and steel corrodes and so monitoring is important," said Professor Fred Worrall, from the Department of Earth Sciences at Durham University, who led the research.

"Overwhelmingly wells are properly decommissioned and our study shows that when methane does leak the levels are low, for example when compared to methane produced by the agricultural use of the land," he added.

Leaks develop early

At one former well at Hardstoft in Derbyshire, gas can be seen bubbling through a puddle at the surface. The Well was drilled in 1917 and abandoned before modern decommissioning regulations were in place. Methane levels here were more than 10 times higher than for average decommissioned wells.

The study found that 40% per cent of the most recent wells surveyed showed leaks.

This suggests that leaks develop early in the life of a decommissioned well.

It also found that methane levels did not increase significantly with the age of the well since drilling.

Water supply impact?

The research did not examine the implications of methane leaks on the water supplies. In the US concerns have been raised about elevated levels of methane in water near fracking wells.

The British Geological Survey is undertaking a National Baseline Methane Survey of groundwaters across the UK.

Understanding the current groundwater levels of methane will provide a baseline against which any future changes could be measured.

The research into methane leakage, led by the Durham University, is published on Tuesday in the journal "Science of the Total Environment".

It is part of work carried out by the ReFINE project - which is led by Durham & Newcastle Universities - and which focuses on researching the potential risks of shale gas and oil exploitation.

The project has been funded by UK research councils and agencies as well as firms involved in oil and gas exploration and fracking including Shell, Chevron, Ineos and Centrica.

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