A ‘fracking’ technique to extract gas from the ground was the ‘highly probable’ cause of earth tremors on the UK’s Lancashire Fylde coast.
On April 1 one tremor of magnitude 2.3 on the Richter scale hit the area followed by a second of magnitude 1.4 on May 27, prompting locals and environmental campaigners to blame the fracking technique being used locally by oil and gas firm Cuadrilla. The company commissioned a report by independent experts to investigate any links between the tremors and fracking work at their Preese Hall-1 well in Lancashire.
Fracking involves extracting gas reserves from underground by a process of hydraulic fracturing of shale rock using high pressure liquid to release gas - a process green groups claim is damaging the environment.
Today a summary published by the company said it is probable the fracking caused the tremors. It said: "The report concludes that it is highly probable that the fracking at Preese Hall-1 well triggered the recorded seismic events.
"This was due to an unusual combination of factors including the specific geology of the well site, coupled with the pressure exerted by water injection.
"This combination of geological factors was rare and would be unlikely to occur together again at future well sites.
"If these factors were to combine again in the future, local geology limits seismic events to around magnitude 3 on the Richter scale as a worst-case scenario."
The report said a "number of factors coincided to cause the seismic events".
First, the gas well encountered a "pre-existing critically stressed fault" which "accepted large quantities of fluid", and the fault was "brittle enough to fail seismically".
The two tremors were "most likely" induced by "repeated direct injection of fluid into the same fault zone", the report states.
But it goes on to say the probability of a repeat occurrence of a "fracture-induced seismic event" with similar magnitude is "very low".
The report was published at 9am today, hours after protesters stormed the firm's gas exploration site.
Environmental campaign group Frack Off entered the shale gas rig at Banks, near Southport, at around 5.30am.
The report, titled Geo-mechanical Study Of Bowland Shale Seismicity, was commissioned by Cuadrilla Resources and carried out by a team of independent experts from across Europe, according to the company.
The report goes on to say the water-injection fracking technique is used more than 3km (about two miles) below ground and this "significantly reduces the likelihood of a seismic event of magnitude 3 or less on the Richter scale having any impact at all at the surface".
The theoretical maximum seismic event of magnitude 3 would not present a risk to personal safety or damage to property on the surface, the report states.
It proposes an "early detection system" to monitor seismic activity at Cuadrilla's drilling site which would "build in an extra layer of safety".
It proposes steps to reduce the chance of further tremors "exceeding safe limits".
Fracking has also been blamed on spoiling water supplies by fluid used in the process seeping into underground waterways.
The report states fracking carried out by Cuadrilla in the Bowland basin occurs at a depth of around 3km, whereas groundwater aquifers do not exist beyond a depth of around 300 metres (1,000 feet).
The Frack Off protest at Cuadrilla's drilling site was timed to "highlight the hypocrisy" of the Shale Gas Environmental Summit in London today.
The campaign group said the event, sponsored by companies involved in the oil and gas industry, will try to promote rapid expansion into the untapped fossil fuel.
Campaigners are also expected to stage a "Frack Mob" mass event outside the summit at 3pm.
At the drill site in Lancashire six protesters climbed up the rig to erect a banner before police were called.
A spokeswoman for Lancashire Police said: "At around 5.30am around seven protesters gained entry to the Cuadrilla gas drilling site in Banks.
"Six out of the seven have climbed up a rig on the site and have erected a banner.
"One protester remains on the ground. Police are in attendance and a cordon has been put in place around the site. We are liaising with the site owners and the protesters to bring about a peaceful resolution."
A spokesman for the company said they were assessing the situation and police had sealed off the rig.
Frack Off spokeswoman Jenny Boykin said: "Fracking uses huge amounts of water mixed with toxic chemicals, a large fraction of which are never recovered.
"The fracking fluid also leaches chemicals like arsenic out of the rocks when it is used, making it even more toxic, and so the fluid that is recovered becomes a big disposal problem.
"The contamination of irrigation water means that everyone's food supplies could potentially be affected. Fracking in the United States has already resulted in numerous spills of these fluids."
A spokesman from the Department of Energy and Climate Change said: "Cuadrilla's geomechanical study was given to the Department of Energy and Climate Change today.
"The implications of this report will be reviewed very carefully - in consultation with the British Geological Survey, independent experts, and the other key regulators, HSE and the Environment Agency - before any decision on the resumption of these hydraulic fracture operations is made."