Man-made earthquake risk reduced if fracking is 895m from faults
Induced earthquakes
Research lead author Miles Wilson, a Ph.D. student in Durham University’s Department of Earth Sciences, said: “Induced earthquakes can sometimes occur if fracking fluids reach geological faults. Induced earthquakes can be a problem and, if they are large enough, could damage buildings and put the public’s safety at risk.
“Furthermore, because some faults allow fluids to flow along them, there are also concerns that if injected fluids reach a geological fault there is an increased risk they could travel upwards and potentially contaminate shallow groundwater resources such as drinking water.
“Our research shows that this risk is greatly reduced if injection points in fracking boreholes are situated at least 895m away from geological faults.”
The latest findings go further than a 2017 ReFINE study which recommended a maximum distance of 433m between horizontal boreholes and geological faults. That research was based upon numerical modelling in which a number of factors, including fluid injection volume and rate, and fracture orientation and depth, were kept constant.
Fault reactivation
Researchers behind the latest study said that changing these parameters might lead to different horizontal extents of fractures from fluid injection points.
The researchers added that this did not mean the modelling results of the previous study were wrong. Instead they said the previous study was approaching the same problem using a different method and the new study provided further context.
In the latest research the researchers used data from previous fracking operations to measure the distance between the furthest detected microseismic event – a small earthquake caused by hydraulic fracturing of the rock or fault reactivation – and the injection point in the fracking borehole.
Shale rock
From the 109 fracking operations analyzed, the researchers found that the horizontal extent reached by hydraulic fractures ranged from 59m to 720m.
There were 12 examples of fracking operations where hydraulic fractures extended beyond the 433m proposed in the 2017 study.
According to the new study, the chance of a hydraulic fracture extending beyond 433m in shale was 32 per cent and beyond 895m was one per cent.
The research also found that fracking operations in shale rock generally had their furthest detected microseismic events at greater distances than those in coal and sandstone rocks.
Shale gas and oil exploitation
Microseismic data was used in previous Durham University research from 2012. This suggested a minimum vertical distance of 600m between the depth of fracking and aquifers used for drinking water, which now forms the basis of hydraulic fracturing regulation in the UK’s Infrastructure Act 2015.
Professor Richard Davies, Newcastle University, who leads the ReFINE project, said: “We strongly recommend that for the time being, fracking is not carried out where faults are within 895m of the fracked borehole to avoid the risk of fracking causing earthquakes and that this guideline is adopted world-wide.”
ReFINE is led jointly by Durham and Newcastle Universities and has been funded by the Natural Environment Research Council (UK), Total, Shell, Chevron, GDF Suez, Centrica and Ineos.
Working closely with a global network of leading scientists and institutions, ReFINE focuses on researching the potential environmental risks of hydraulic fracturing for shale gas and oil exploitation.
— Read more in M. P. Wilson et al., “Fracking: How far from faults?” Geomechanics and Geophysics for Geo-Energy and Geo-Resources (28 February 2018) (doi: org/10.1007/s40948-017-0065-3)
