Speakers at the UK shale gas conference express concern over the extent of drilling that would be required to exploit shale gas

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Prof Andy Aplin, a former adviser to oil giant BP and now at Durham University, said that exploiting the Bowland shale, based on the example of the US, might require 33,000 wells.

"What we are looking at here is a massive increase in the number of wells if we are going... to exploit this resource to the extent to which our political masters would like us to do, from the Treasury's point of view," he said.

The researchers underlined the fact that there was a significant lack of data about UK shale formations. There were many questions still outstanding, including the impact of fracking fluid on seismic faults.

"These reservoirs are really complicated, they are much larger and more complex on any spatial scale compared to our North Sea reservoirs - we should not pretend we know very much about the nature of the UK reservoirs today," said Prof Aplin.

The issue of the number of wells was also commented on by Lord Oxburgh, former chairman of Shell and a member of the House of Lords Select Committee on Science and Technology.

The experience in the US suggests that the output of shale gas or oil from fracked wells declines very quickly, increasing the need to drill new wells.

"The rate of flow drops by 85% over three years, a conventional well could still be getting high flow rates after 30 years," he said.

"There are other limiting factors in the UK, including the size and density of the population. And the process of fracking was extremely noisy.

"I think it is going to be a limiting factor near towns, these are brutes, these big pumping machines."