Felt seismicity associated with shale gas hydraulic fracturing: The first documented example in Europe

Abstract

We describe the origin of felt seismicity during the hydraulic fracturing of the Carboniferous Bowland Shale at the Preese Hall 1 exploration well near Blackpool in the UK during 2011. The seismicity resulted from the interaction of hydraulic fracturing and a fault, the location of which was unknown at the time but has subsequently been located and does not intersect the well borehole. Waveform cross correlation is used to detect 50 events in the sequence. A representative hypocenter and strike-slip focal mechanism is calculated using the best recorded seismic event. The hypocenter is calculated to lie 300-400 m east, and 330-360 m below the injection point and shown to lie on a fault imaged using 3-D seismic at a depth of about 2930 m. The 3-D survey shows that not only the event hypocenter but also the focal mechanism correlates strongly with a subsequently identifiable transpressional fault formed during the Late Carboniferous (Variscan) basin inversion.

Horizontal respect distance for hydraulic fracturing in the vicinity of existing faults in deep geological reservoirs: a review and modelling study

“…It is possible that all of these are correct depending on the exact nature of the fault, the fracture intensity and its closeness to criticality. The maximum respect distances then range from 63 to 433 m, which is within the horizontal distance range (300-400 m) that the reactivated fault was calculated to be from the injection point at Blackpool (Clarke et al 2014).…”

“…This allows the location of fracturing to be identified and provides a means of tracking the efficiency, and the spatial and temporal progress of the hydraulic fracturing. These events normally have magnitudes below zero (Maxwell 2013;Verdon et al 2010); however, since 2011, there have been several recorded examples of seismicity at magnitudes greater than 2.0 (Holland 2013), of which three (BC Oil and Gas Commission 2012; Clarke et al 2014;Schultz et al 2015) were felt and reported by local populations. In at least one of these cases (Clarke et al 2014), hydraulic fracturing has influenced a preexisting fault causing it to slip to a sufficient extent and length to produce a felt earthquake.…”

“…Felt seismicity occurring near Blackpool, Lancashire, UK (Clarke et al 2014), was associated with the first fracked well for shale gas in the UK, commencing just before and during the second stage of hydraulic fracturing and, as such, has become of considerable interest to all parties in the shale gas debate. Analysis of the seismicity shows that these felt events were caused by fluid injection reactivating preexisting faults (Clarke et al 2014).…”

“…Analysis of the seismicity shows that these felt events were caused by fluid injection reactivating preexisting faults (Clarke et al 2014).…”

“…In Ohio, USA, another area where deep well fluid injection has caused seismicity (Kim 2013), hydraulic fracturing operations in at least two separate areas have caused events including a Mw 2.2 (Friberg et al 2014) and a ML 3.0 (Skoumal et al 2015). The first documented account of felt seismicity from hydraulic fracturing for shale gas in Europe was near Blackpool, UK (Clarke et al 2014;Eisner et al 2013) and included a ML 2.3 event. Of these examples three were felt: Blackpool, Ohio and Oklahoma.…”