The following is an adapted extract from a research piece entitled 'The future of UK shale gas" and is second in a series on environmental concerns related to fracking.
Cuadrilla suspended drilling after a series of tremors near its Preese Hall site, which has been operational since 2011. This moratorium was subsequently revoked in December 2012, allowing exploratory drilling to resume. Following tremors within the vicinity of the well, the Department of Energy and Climate Change (DECC) introduced further regulation in order to reduce the risk of a similar occurrence. Operators are now required to assess fault lines prior to drilling, monitor seismic activity during the hydraulic fracturing and consult with the DECC on appropriate places to 'frack' based on British Geological Survey (BGS) records. Further response to the seismic activity at Preese Hall included installing a nearby monitoring station and giving the British Geological Survey National Earthquake Monitoring System the role of continuous monitoring of seismic activity.
University of Durham research published in 2013 dispels the notion that seismic activity associated with hydraulic fracturing is environmentally damaging or unusual for energy industry norms. The research, entitled "Induced Seismicity and the Hydraulic Fracturing of Low Permeability Sedimentary Rocks", concluded:
"In almost all cases, the seismic events caused by hydraulic fracturing have been undetectable other than by geoscientists. It is also low compared to other manmade triggers. Earthquakes caused by mining can range from a magnitude of 1.6 to 5.6, reservoir filling from 2.0 to 7.9 and waste disposal from 2.0 to 5.7.
By comparison, most fracking-related events release a negligible amount of energy roughly equivalent to or even less than someone jumping off a ladder onto the floor..."
A study published in Marine and Petroleum Geology found only 3 earthquakes which could be felt by humans have been caused by hydraulic fracturing, despite over a million wells being drilled worldwide. A prominent US report published in Science used seismicity and hydrogeological models to associate quakes with the disposal of wastewater, rather than the process of hydraulic fracturing itself. In the US, injection wells are utilised by the energy sector to dispose of waste fluids produced through extraction. These injection wells have been associated with earthquakes in Texas, Arkansas and Ohio in the States. In telephone correspondence with the EA, it was confirmed that wastewater from Preese Hall (the only UK site 'fracked', as opposed to test drilled) was disposed of using an authorised contamination plant (in this case, Davyhulme treatment works) and there had yet to be any applications to utilise deep injection wells for wastewater disposal in the UK.
The absence of deep injection wells for wastewater disposal suggests earthquakes will not hinder shale gas' future in the UK. Whilst hydraulic fracturing is associated with seismic activity under 3 on the Richter scale, Cuadrilla's 'Geo-Mechanical Study of Bowland Shale Seismicity' found quakes above 3 were "extremely rare". The operator cited an "unusual combination of geology" which was "unlikely to occur together again at future well sites". The DECC remains adamant that the process of hydraulic fracturing does not increase the likelihood of earthquakes in the long-term. The Durham Energy Institute collated data from nearly 200 cases of induced seismicity from 1929 onwards and found that mining accounted for 77 of the cases, reservoir formation for 39, geothermal energy generation for 21, whilst oil and gas fields were only responsible for 42 cases.
The tremors at Preese Hall and earthquakes in the US should not be used to denigrate hydraulic fracturing. Geological anomalies contributed to the tremors in Lancashire to occur and it is disingenuous to suggest that tremors like these would become a regular occurrence. The largest tremor at Preese Hall registered 2.3 on the Richter scale; over a million of quakes on this scale occur worldwide every year and it is minimal compared with other industries. Nor is it true that larger earthquakes that are more common in the US (notably in Oklahoma and Ohio) would occur as a result of fracking in the UK. These are associated with the injection of wastewater back into the rock, rather than fracking itself, which is an improbable practice in the UK.