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Characterising the vertical separation of shale-gas source rocks and aquifers across England and Wales (UK)

Fig. 1a Schematic diagram showing potential source-pathway-receptors resulting from shale gas exploration and production (after Vengosh et al. 2014). Numbers correspond to pathways described in the text. Diagram not to scale. b Schematic diagram illustrating the effect of aquifer–shale separation distances and potential direct pathways through the intervening interval, including migration through the intervening rock mass, and aquifer and hydraulic fractures linking with a permeable fault zone. Green dotted lines illustrate 100 and 600-m hydraulic fracture heights

The application of the method is then demonstrated for two of these pairs—the Cretaceous Chalk Group aquifer and the Upper Jurassic Kimmeridge Clay Formation, and the Triassic sandstone aquifer and the Carboniferous Bowland Shale Formation. Challenges in defining what might be considered criteria for ‘safe separation’ between a shale gas

Fracking: How far from faults?

Fig. 4 Map showing the epicentre of the fracking-induced earthquake of 2nd August 2011 (PH Event) in relation to the hypothesised fault which slipped and the orientations of the maximum (SHmax) and minimum (SHmin) horizontal stress directions. Adapted from Clarke et al. (2014).

An alternative approach is to use microseismic data to infer the extent of fracture propagation and stress changes. Using published microseismic data from 109 fracking operations and analysis of variance, we find that the empirical risk of detecting microseismicity in shale beyond a horizontal distance of 433 m is 32%