Leaks from faulty shale gas and oil wells have contaminated water supplies, but fracking itself is not to blame, scientists say 

The film Gaslands showed drinking water contaminated by methane pollution

The film Gaslands showed residents near fracking sites who were able to set alight to the water from their taps, apparently due to methane contamination.

By  Emily Gosden, Energy Editor

Leaks from faulty shale gas and oil wells have contaminated water supplies, but fracking itself is not to blame, according to new research.

Fracking involves drilling a well deep underground and then pumping water, sand and chemicals down it at high pressure to fracture the rocks, enabling shale gas or oil trapped within them to flow out.

Critics of the controversial process have often claimed that it pollutes water supplies, citing examples of contamination at shale gas sites in the US.

The 2010 film Gaslands showed residents near fracking sites who were able to set alight to the water from their taps, apparently due to methane contamination.

In a paper published in the journal Proceedings of the National Academy of Sciences, scientists analysed the origins of the gas in contaminated water by shale wells in Pennsylvania and Texas, two of the biggest drilling regions in the US.

They found that the fracturing of the rocks was not to blame for the leaks. Instead, botched construction of the wells led to gas or oil escaping through cracks in metal casing or through faulty cement seals.

Thomas H Darrah, assistant professor of earth science at Ohio State, who led the study, said: "Our data clearly show that the contamination in these clusters stems from well-integrity problems such as poor casing and cementing.

"The good news is that most of the issues we have identified can potentially be avoided by future improvements in well integrity."

Avner Vengosh, professor of geochemistry and water quality at Duke, said: "These results appear to rule out the possibility that methane has migrated up into drinking water aquifers because of horizontal drilling or hydraulic fracturing, as some people feared."

The distinction is important because it suggests fracking is not intrinsically polluting and should be able to take place safely if wells are constructed properly.

Problems of faulty well construction can also lead to leaks from conventional oil and gas wells.

However, extracting gas from shale requires a far greater intensity of wells than conventional drilling.

Ministers in the UK insist that the regulatory regime is far stricter in the US and should prevent such leaks.

But critics say there are insufficient safeguards to ensure the process is conducted safely and are likely to seize on the study as further evidence that shale gas exploration can be damaging.

Robert B. Jackson professor of environmental and earth sciences at Stanford and Duke, one of the report's authors, said: "People's water has been harmed by drilling. In Texas, we even saw two homes go from clean to contaminated after our sampling began."

The findings echo those of a study by Researching Fracking in Europe (ReFINE), backed by the British Geological Survey and published earlier this year, which also found that although shale gas wells can leak, fracking itself was not to blame. Problems with the structure of the wells – such as inadequate cement seals - were responsible.

ReFINE found that more than six per cent of wells in a major shale exploration region in Pennsylvania had reported some kind of leak.

Professor Richard Davies of Durham University, one of the report’s authors, told the Telegraph at the time: "We have not found any evidence that fracking is the problem. It’s the boreholes that could cause water contamination, and emissions into the atmosphere.

“Shale gas requires a lot of wells to be drilled; more wells to produce the same volume of gas from shale as from a conventional reservoir. That’s why well integrity is critical.”

The study found that of 143 wells that were in use in the UK in 2000, one had leaked. But it found this was “likely to be an underestimate of the actual number of wells that have experienced integrity failure” because of lack of data.

www.telegraph.co.uk