Tremor threshold to be set before shale gas ‘fracking’ resumes

The company involved has accepted stringent recommendations from government-commissioned experts who say hydraulic fracturing should be allowed to continue at the Preese Hall well in Lancashire.

One proviso is that even a tremor too small to be noticed above ground should result in an immediate shutdown. Remedial action would then have to be carried out before work is resumed.

The independent report, published today, also calls for careful monitoring of the site using arrays of seismic sensors, and steps to ensure excess pressure cannot build up beneath the ground.

Hydraulic fracturing, or “fracking”, involves injecting high pressure water and chemicals into shale rock to release trapped natural gas.

Well operator Cuadrilla Resources estimates that the Bowland Basin prospect site in Lancashire contains as much as 200 trillion cubic feet of gas. Even if only a fraction of this can be extracted, it still represents a very significant energy resource.

On April 1 and May 27 last year, two small earthquakes – of magnitude 2.3 and 1.5 – occurred near Blackpool. No damage was caused, although several people called the police to report shaking. After a second tremor was linked to fracking, operation of the Cuadrilla well was halted.

The events led to public protest, with one group scaling a test drilling rig in Lancashire.

Later independent experts appointed by Cuadrilla concluded that both tremors were triggered by fracking and proposed a “traffic light” early warning system.

Yesterday’s report, commissioned by the Department of Energy and Climate Change (DECC), confirmed that the earthquakes were caused by fracking taking a geologically stressed and vulnerable area.

The authors, Dr Christopher Green, from GFrac Technologies, Professor Peter Styles, from Keele university, and Dr Brian Baptie, from the British Geological Survey, said further fracking-induced earthquakes were possible, but a six-week consultation period now follows before a decision is taken.

DECC chief scientific advisor David MacKay said: “If shale gas is to be part of the UK’s energy mix we need to have a good understanding of its potential environmental impacts.”