Monday, 17 December 2012

Ed Davey's Written Statement on Shale Gas: Highlights

Well done if you got to the end of my previous post, Ed Davey's full statement on shale gas extraction. In case you didn't, I've selected the highlights with respect to induced seismicity:

I have concluded that appropriate controls are available to mitigate the risks of undesirable seismic activity. Those new controls will be required by my Department for all future shale gas wells.
 So any new regulations will be applied to all wells.
the amount of energy likely to be stored in these faults is not large, and the largest earthquake likely in this area from such a cause is assessed at magnitude 3.
Seems reasonable that the maximum likely quake is the same as those typically seen in background rates.
Operators will first be required to review the available information on faults in the area of the proposed well to minimise the risk of activating any fault by fracking, and required to monitor background seismicity before operations commence. Real time seismic monitoring will also continue during operations, with these subject to a “traffic-light” regime, so that operations can be quickly paused and data reviewed if unusual levels of seismic activity is observed.
Very interesting, and good news for service companies. The 'available information' on faults in the area must surely imply 3D seismic surveys prior to any fracking. Good news if you are WesternGeco et al. Also, real time (micro)seismic monitoring is required. Good news for microseismic companies (and researchers like me).
Real-time recording of earthquakes during and for 24 hours after each stage of the frac will be analysed to look for abnormal induced events amidst the normal background seismicity.
Again, more good news on real time monitoring. I'm not sure how we'd classify an 'abnormal' event though.
Operators will also be required to monitor the growth in height of the frac away from the borehole. This will allow the operator to evaluate the effectiveness of the frac, but also ensure that the actual fracture is conforming to its design, and that it remains contained and far away from any aquifers.
To monitor the growth in height of the fracture will require accurate microseismic monitoring, with depths in particular being well constrained. This means deployments of significant arrays. Chucking a couple of broadband seismometers nearby will not be sufficient - large dense surface arrays or downhole arrays will be required.
the remedial action level for the traffic light system (that is, the “red light”) will be set at magnitude 0.5 (far below a perceptible surface event, but larger than the expected level generated by the fracturing of the rock).
Cuadrilla's 'traffic light' system will remain in place. This states that fracking must stop if an event larger than M0.5 is induced. In principle this is a sensible limit. However, it throws up questions of it's own, because in science there are such things as error bars. There's no such thing as an M0.5 event. There's M0.5 ± some value. There are also several different ways of computing magnitude, which don't always produce the same value. The question is then: do you take the highest possible value, the lowest possible value, or some mean (most probable) value as the point at which the traffic light red is exceeded?

And who gets to decide? Industry themselves? Probably not the wisest move. DECC themselves? Do they have the expertise - not really? <begins shameless self promotion> how about independent academic experts?< /ends shameless self promotion>

All told, good news for shale gas companies looking at the UK, but even better news for service companies (and researchers) with experience in microseismic monitoring!  

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