- Preece Hall shale gas fracturing review & recommendations for inducing seismic mitigation (April 2012)
A series of studies were commissioned by Cuadrilla Resources Ltd to examine the possible relationship between hydraulic fracture operations at the Preese Hall well, near Blackpool, and a number of earthquakes which occurred in April and May 2011, the largest of which had a magnitude of 2.3 ML. The reports from these studies conclude that the earthquake activity was caused by direct fluid injection into an adjacent fault zone during the treatments, but that the probability of further earthquake activity is low. The reports analyse the earthquake activity and use available geological and geophysical data, including background geology, well logs and core samples, along with fracture treatment data, to develop a conceptual geomechanical model. A numerical model consisting of a single fault plane in a rock matrix was used to simulate the induced seismicity, compare with observations, and estimate maximum magnitudes for induced earthquakes. A critical magnitude at which damaging ground motions might occur was estimated using the German DIN4150 standard, and a simple relationship suggested for ground motions as a function of magnitude and distance. Finally, a protocol for controlling operational activity is proposed. This builds on extensive Enhanced Geothermal System experience and uses a traffic light system based on real-time monitoring of seismic activity.