Engineering news
A controversial “fracking” technique to extract gas from the ground was the “highly probable” cause of earth tremors which hit Lancashire's Fylde coast earlier this year, a report concluded today.
One tremor of magnitude 2.3 on the Richter scale hit the area on 1 April followed by a second of magnitude 1.4 on 27 May, prompting locals and environmental campaigners to blame the fracking technique being used locally by oil and gas firm Cuadrilla.
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 claims is damaging the environment.
The firm commissioned a report by independent experts to investigate any links between the tremors and fracking work at their Preese Hall-1 well in Lancashire.
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, 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 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).