UK offshore reserves of shale gas could exceed one thousand trillion cubic feet (tcf), compared to current rates of UK gas consumption of 3.5 tcf a year, or five times the latest estimate of onshore shale gas of 200 trillion cubic feet.
Reserves on this scale would put the UK in the top 20 countries with the highest shale reserves, and 1,000 tcf would approach estimates for China, the US and Argentina.
There are still no reliable figures available for the UK, and some experts doubt preliminary onshore reserve figures by private companies. Also only around 10-20% of total reserves are currently deemed recoverable.
But some experts say that the final recoverable reserve figure is likely to be big enough to make Britain energy self-sufficient.
“There will be a lot more offshore shale gas and oil resources than onshore,” Nigel Smith at the British Geological Survey (BGS) said. UK offshore reserves could be 5-10 times as high as onshore, he said.
On Tuesday (17 April), a UK government report backed the drilling of shale gas onshore after a temporary ban on the controversial extraction technique known as hydraulic fracturing, or fracking.
Britain has long-established offshore development experience through its North Sea oil and gas sector and Smith said that already available offshore geological data showed that offshore shale deposits were more abundant than their onshore equivalents.
He told a British parliamentary committee that Britain could become energy self-sufficient if it went offshore with its unconventional oil and gas industry.
The committee recommended that the UK government encourage the development of the shale gas industry and “explore the impacts of tax breaks to the sector.”
“We have potentially huge volumes [of shale] present in the subsurface - the volumes are mind-blowingly big,” said Melvyn Giles, global head of unconventional gas and light tight oil at Shell.
“The figures appear to suggest the shale resources are so large that the question is not how much is out there, but how much can be retrieved - how much can be economically accessed in an environmentally acceptable way,” he added.
Shale is soft, finely stratified sedimentary rock that formed from consolidated mud or clay. Hydraulic fracturing is the process of creating small cracks in underground rock formations up to 7,700 meters below ground level to extract gas (and oil) from shale.
Energy services company Schlumberger said in a research report that there are large shale gas and oil reserves in the North Sea - along the German, Dutch and Danish coasts - as well as in the Baltic Basin.
Much of the development in Europe may focus offshore after onshore exploration hit setbacks when France and Bulgaria banned exploration over concerns about ground water pollution. Poland, previously thought to be a European leader, recently slashed its reserves estimates by 90%.
However, as well as being expensive and methane-heavy, environmentalists argue that fracking has caused earth tremors in northern England and polluted ground water sources in the US.