A REPORT PUBLISHED BY DECC that includes a BGS co-author concludes that the earthquakes near Blackpool in April and May 2011 were induced by hydraulic fracture treatments at the Preese Hall well (PH1), operated by CUADRILLA RESOURCES LTD. The report also concludes that further small earthquakes cannot be ruled out, however the risk from these earthquakes is low, and structural damage is extremely unlikely.
The report also recommends a number of measures to reduce the likelihood of earthquakes associated with hydraulic fracturing in future. These include :
On 1 April and 27 May 2011, two earthquakes with magnitudes of 2.3 ML and 1.5 ML were detected in the Blackpool area. These earthquakes were immediately suspected to be linked to hydraulic fracture injections at the Preese Hall well, operated by Cuadrilla Resources Ltd. This well was hydraulically fractured during exploration of a shale gas reservoir in the Bowland basin. As a result of the earthquakes, operations were suspended at PH1 and Cuadrilla Resources commissioned a number of studies into the relationship between the earthquakes and their operations.
There are numerous examples of induced earthquakes in hydrocarbon fields (e.g. SUCKALE, 2010) and Enhanced Geothermal Systems (e.g. MAJER ET AL, 2007). Induced micro-seismicity during hydraulic fracture treatment is commonly used to image fracture networks and estimate stimulated volumes. Magnitudes of the earthquakes during hydraulic fracture stimulation in reservoirs such as the Barnett Shale are typically less than 1 ML. This suggests that the earthquake activity observed at Preese Hall is rather unusual.
However, both the tectonic history and the present-day STRESS REGIME in the British Isles is rather different to many of these areas of exploration and production. Also, it should be noted that many US shale gas plays are in relatively remote locations, with no monitoring networks in place. A recent study by HOLLAND (2011) suggests that hydraulic fracturing induced seismicity may be a potential issue for other reservoirs. There are also examples of seismicity induced by fluid disposal in deeper wells (e.g. FROHLICH ET AL., 2011).