Issue 13: Can the disposal of waste fracking fluids by underground injection cause earthquakes

Yes. These earthquakes have been more problematic and dangerous than earthquakes associated with hydraulic fracturing itself. However, disposal of waste fracking fluids in the UK is extremely unlikely and recycling of fluids is becoming the norm.

On Wednesday (4th September 2013) NBC News reported that scientists had linked 109 earthquakes in Ohio to hydraulic fracturing. 

What happened?

NBC reports that "...the earthquakes were never very powerful and caused no serious injuries or damages". However, the fact that they occurred in a region not known for seismicity was an indicator that they might be linked to human activity. The largest (shown in the image) was about magnitude 4, but the others were all much smaller. Counting the number of earthquakes is therefore a misleading statistic if we want to judge the impact of a set of earthquakes.

The earthquakes were caused by the injection of waste hydraulic fracturing fluid into a deep disposal well.

In fact Ohio has 177 wells into which it pours waste water from diverse sources. The practice is highly dangerous if it is carried out without a proper understanding of the local geology and if the volumes and fluid pressures are not well regulated. That seems to be what has happened here.
 

The largest Ohio earthquake (Courtesy of USGS)

The earthquakes were only associated with one of the 177 waste water disposal wells and although that was probably disposing of waste hydraulic fracturing fluids, the earthquakes were not related to the processes of  shale gas exploration, drilling or hydraulic fracturing itself. The scientists noted that since only this one well was linked with seismic activity, the capability of waste water injection to cause earthquakes was rare. 

But not that rare. The previous week residents in Greenbrier, Arkansas settled a suit for minor damages caused by earth-quakes triggered by under-ground injection of waste water.

The disposal of waste fracking fluids by underground injection is currently unregulated in the USA, although the EPA have said that rules will be in place by 2014. It is, actually, rather important. The largest earthquake ever recorded in Oklahoma occurred in 2011, as one of a pair with magnitudes 4.7 and 5.6, which were caused by waste fluid injection. There were two injuries, 14 buildings were destroyed and others damaged together with a road. 

The Oklahoma earthquake (Photograph by Sue Ogrocki, AP)

There is no guarantee that larger earthquakes due to waste water injection will not occur if the procedure is not tightly regulated. This is because the waste water injection is only the trigger to the earthquake; the size of the earthquake itself depends upon the amount of stored energy in the stressed fracture prior to triggering.

In fact the problem may be resolving itself. In Europe the intention is to recycle all fracking fluids. Even in the USA, there has been a steady swing away from the injection of waste fracking fluids for disposal towards recycling. Currently, fracking fluid is treated and then reused in other fracking jobs, but the technology exists to transform the fracking water into water that meets the standards required for being released back into the surface water.

Could earthquakes caused by waste water injection happen in the UK?

No. 

• Unregulated injection of any fluid for disposal is not allowed under UK and EU regulations. The chances of obtaining permission to do so with ordinary water would be almost zero, and it would never be considered for waste fracking fluids, especially as they can be efficiently recycled these days.
• Geophysicists have known for a very long time that fluid injection can cause earth tremors. It should never be carried out without mapping local major faults and monitoring the back-ground seismicity, and should never exceed certain volumes and fluid pressures. This is all taken account of in the UK regulations and practices associated with shale gas.
• The UK recommendations are that all processes should be stopped if an event greater than magnitude 0.5 occurs. This level is about five million times less destructive than the largest of the Ohio 'quakes based on energy release.

Does that mean no earthquakes from shale gas and fracking in the UK?

No. 

If there is development of the shale gas industry in the UK, I would still expect there to be a small increase in the number of small (less than magnitude 2) earth tremors associated with the fracking process. 

These tremors will not result in damage to property or injuries, and it is very unlikely that you will ever feel one.