I wrote this story for the Guardian but more information came to my attention after it was published, and I felt that the way the piece was edited made it seem supportive of iGas, their misleading claims, and shale gas extraction. So I have published a different version here. For the Guardian version see here.

Energy company iGas  announced on Monday that its estimates of shale gas resources are considerably higher than previously thought, but environmentalists say the figures are misleading.

Studies by the company show its licensed areas in north-west England hold between 15 and 170 trillion cubic feet (tcf) of shale gas – with a most likely scenario of 102 tcf – in an area covering 300 square miles across Cheshire. However these figures represent ‘gas in place’ rather than actual reserves, with only a fraction of this figure being recoverable.

iGas claimed its estimates could mean reduced reliance on imported gas for the UK. Andrew Austin, iGas’s chief executive, said that the study supports their view that “these licences have a very significant shale gas resource with the potential to transform the company and materially benefit the communities in which we operate.”

The announcement comes after promises by the chancellor George Osborne to give tax breaks to the shale gas industry, and the lifting of restrictions last December on the controversial practise of ‘fracking’ – hydraulically fracturing of shale rock to extract the gas – following earthquakes near Blackpool linked to the method.

Rival shale gas firm Cuadrilla, which has the former BP boss Lord Browne on its board, said in 2011 that it estimated its own reserves in the region at 200 tcf. Its chief executive, Mark Miller, said at the time that 10-30% of that would likely be extracted.

The UK’s annual gas consumption currently stands at around 3 trillion cubic feet. Mr Austin said that based on these estimates, combined with North Sea reserves, the UK could be self sufficient in gas for years to come.

But the new estimates from iGas were met by scepticism by green groups, which have opposed the development of shale gas in the UK on the grounds that it would squeeze out investment in renewable energy, release more climate-warming carbon into the atmosphere , pollute water supplies and ruin chances of meeting emissions targets.

Doug Parr, Greenpeace Chief Scientist and Policy Director, said: “Deciding how much gas there is based on the word of a shale gas firm is like buying a second hand car without lifting up the bonnet and asking the price. iGas may be keen to impress its investors in China but these figures are just hype. The world’s largest oil and gas firms were attracted to Poland by similar claims – now they are rushing to leave.”

‘Every analyst, from Poyry, to Ernst and Young and even Cuadrilla says UK shale will have little or no impact on bills. MPs voting tomorrow on the decarbonisation of the power sector should remember that sending drilling rigs into our rural villages in a desperate hunt for gas could cost them votes. They should instead vote for clean, renewable energy that will bring bills down over time.’

Parr is also sceptical about the accuracy of the estimates, which range over an order of magnitude. “The huge range indicates that they don’t have a tight understanding of how much there actually is – this is very much in the realms of speculation.

The figures represent ‘gas in place’ rather than actual reserves – a figure often used by the industry but which can be misleading as such as a small proportion of this gas is actually extractable.

“It’s unknown how much of these reserves will actually be recoverable – at best it will be a small fraction, possibly none at all, ” says Parr.

Recovery rates of 10-30% based on US figures are often used as estimates for what could be recovered from UK reserves, however some geologists suspect idiosyncrasies of UK geology means that well productivity in this country is likely to be much lower.

The iGas figures were arrived at by generating vibrations at the surface and interpreting their subsurface reflections to create a 3D map of the subsurface morphology – so-called seismic survey. Cores are then drilled to identify how much gas is in the rock of sample wells. These two data sets are then combined and extrapolated up to provide estimates of how much gas is in place across a wider area.

iGas plan to conduct exploratory drilling later this year to further refine the estimates.

An independent British Geological Survey study is currently being compiled for the Department of Energy and Climate Change. The study is expected in the next few weeks and will independently report how much shale gas there is in the region.

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