Digging into the earth in search of her treasures is as old as time itself. Deep in our psyche lies the notion that the earth’s minerals lie in neat seams underneath the soil to be scooped out for further use as and when needed.
In reality nothing could be further from the truth. Gold mining is a good example. The purest forms of unprocessed gold, the type most of us would recognise as gold on a wedding ring, is found not in under-ground seams but on river-bed and that supply was exhausted centuries ago.
In reality, for every tonne of rock mined a mere 1.5 grams of gold can be extracted. Remaining gold deposits are typically dispersed in fine particles over a wide area of rock – like a shower of fine gold-dust blown into the earth by Tinkerbelle.
In many ways shale gas extraction is not dissimilar to gold mining. Unconventional gas is held rigid in the shale rock formations making the free-flow of the natural gas to the well head impossible. To release the trapped treasure industry needs to frack.
Fracking is not without its consequences and one of the more alarming aspects of underground hydraulic fracking are the alleged tremors it is said to cause.
A report prepared by the International Energy Association in 2012 (p 26) suggested the earthquakes associated with fracking , “were small, of a magnitude of around two on the Richter scale, meaning they were discernible by humans but did not create any surface damage.”
An on-line site sponsored by industry, Shale Gas Europe, states that “Only in extremely rare circumstances can hydraulic fracturing cause seismic events at ground level. These events are extremely minor, causing no property damage or human harm.” Nigel Lawson, a well known lobbyist for the energy industry, claims that hydraulic fracking causes “barely perceptible tremors – no worse than a heavy lorry passing by your house”.
There are two causes of seismic activity. The first is the process of hydraulic fracturing itself. The second results from injecting waste water into special wells. According to a study prepared for the European Commission to identify potential risks arising from fracking, the risk of seismic activity is low. The study did acknowledge that more significant underground movements could occur as a result of the injection of waste water into wells.
The fact that hydraulic fracturing – either the process itself of the waste water treatment thereof – causes tremors is not in dispute The question is to what extent and how damaging the tremors actually are. Consider the following cases.
On 1st April 2011 the town of Blackpool in Lancashire experienced seismic activity of magnitude 2.3 M. On 27 May 2011 a second seismic activity was recorded measuring 1.5 M. Very low figures indeed and barely perceptible to those above ground. Were it not for the fact that the British Geological Survey’s national seismic network had detected the tremors these incidents may well have gone unnoticed all together. As a result of the tremors Cuadrilla Resources, the company conducting the exploratory drilling in Lancashire, were forced to suspend their operations for one year until the moratorium was lifted in December 2011.
A subsequent report prepared by the Royal Society and the Royal Academy of Engineering reported that in the case of the Blackpool quakes the most likely cause was the transmission of injected fluid into a nearby but previously unidentified pre-stressed fault(own italics). This had the effect of causing the fault to slip and to release its stored energy. In other words, “analysis of the seismic data suggests that the two events were due to the reactivation of a pre-stressed fault.”
Given that the magnitude level was so small does it matter? Possibly not but it is interesting to note that the Royal Society (p 40) states that “UK seismicity is low by world standards,” and “The Blackpool region is an area of low natural seismicity even by UK standards.”
Reports of tremors close to hydraulic fracking sites are also common in the US. On 5th November 2011 the largest ever recorded quake in Oklahoma measuring 5.6M was reported. This did have a perceptible impact on those above ground causing water pipes to burst, a bridge to buckle and reports of “At least 2 people injured, 14 homes destroyed and many damaged in the Shawnee-Sparks area.” Oklahoma, like Lancashire, is not known for being an area of high seismic activity. See this summary from the United States Geological Survey’s (USGS) Earthquake Hazards Programme.
“From 1972-2008 about 2-6 earthquakes a year were recorded by the USGS National Earthquake Information Centre; these earthquakes were scattered broadly across the east-central part of the state. In 2008 the rate of earthquakes began to rise, with over a dozen earthquakes occurring in the region east- northeast of Oklahoma City and southwest of Tulsa, Oklahoma. In 2009 the rate of seismicity continued to climb, with nearly 50 earthquakes recorded–many big enough to be felt. In 2010 this activity continued. The magnitude 4.7 and 5.6 earthquakes of November 5, 2011, are the largest events recorded during this period of increased seismicity. Additionally, the M5.6 quake is the largest quake to hit Oklahoma in modern times.”
A similar, 4.8 M earthquake hit Southern Texas on 20 October 2011. Southern Texas sits above the Eagle Ford Shale where hydraulic fracking is common. As is the case in Lancashire and Oklahoma, Texas is deemed a low risk earthquake zone.
It would appear that the cause of some of the worst tremors associated with fracking relate not to fracking itself but the disposal of the waste water in underground wells – but that will be covered in the following section on water.