Above: Schematic depiction of hydraulic fracturing for shale gas, showing main possible environmental effects (Mikenorton)
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Do you know where your household electricity comes from? There’s a good chance at least some of it is produced by burning fossil fuels, including coal, oil, and natural gas. But how is the fuel extracted before it arrives at a power plant? You’ve probably heard of methods like conventional oil drilling and coal mining. But what exactly is fracking? And why has this particular method attracted so much controversy?
Did you know? China has the world’s largest shale gas reserves, with an estimated 31.5 trillion cubic metres of recoverable gas.Deep underground, over millions of years, large deposits of natural gases like methane have become trapped inside layers of rock. In particular, shale formations are likely to contain vast amounts of natural gas. These deposits are a potential treasure trove of energy, but the extreme depth and impermeability of shale, a rock composed of clay and various other minerals, makes it difficult to access them.
Enter hydraulic fracturing, or fracking. This process involves drilling a well into the rock, usually to depths of over 1500 metres. A mixture of water, sand, and chemicals is injected at extremely high pressure, breaking the rock apart and creating fissures, or cracks, that allow gas to flow to the surface.
Proponents of fracking say it creates jobs, boosts domestic energy production, and makes it possible to tap substantial reserves of natural gas, a fuel that burns cleaner than coal or oil.
So what’s the downside?
The concerns about fracking are largely environmental. Methane is a potent greenhouse gas (GHG), and scientists are worried about its potential impact on global warming. While it currently represents about 13% of Canada’s GHG emissions, methane traps more than 20 times as much heat as carbon dioxide.
Water conservation is another important issue. Fracking a single well typically requires between 8 and 15 million litres of fresh water, almost none of which is recoverable.
There are also concerns about water contamination. Drinking water often comes from the aquifer layer located above shale formations. Normally, this water remains safe from the methane trapped deep below. But fracking creates new pathways in the rock, making it possible for gases to pass between the layers.
Did you know? The rock found in the Marcellus Shale is estimated to be 390 million years old.Industry representatives contend there’s almost no risk of such contamination, since there are typically several hundred feet of impermeable rock between aquifers and the shale deposits. But fracture lengths are unpredictable, especially if they hit naturally occurring fault lines. Improperly sealed pipes can also cause mixing between layers.
When Duke University scientists studied water contamination near the Marcellus Shale in Pennsylvania, they found that 82% of homes close to fracking wells had excessive levels of methane in their drinking water. The concentration of methane increased the closer a home was to the well. In addition, the injection of fracking wastewater back into the ground triggers seismic activity and has been linked to a dramatic rise in earthquakes in the United States since 2010.
Fracking fluid itself is also a bit of a mystery. It’s 99% water and sand, but its exact composition is classified as a “trade secret”, meaning companies don’t have to disclose the formula. So far, 750 different chemicals have been identified in fracking fluid, many of them toxic. The documentary Gasland depicts a 2010 incident in Dimock, Pennsylvania, where fracking was linked to the contamination of 18 water wells with methane, arsenic, barium, and other chemicals.
The hydraulic fracturing industry maintains that contamination has only occurred in rare cases involving improper drilling or defective cement casings (the casings prevent the gas from escaping from the pipes). Tougher water regulations are also being established, and some companies have even developed water-less fracking fluids.
Still, opponents say the risks outweigh the benefits. So for now, the debate continues!
Extracting Natural Gas From Rock (New York Times) Fracking Can Be Done Safely, but Will It Be? (David Biello, Scientific American) Greenhouse Gas Sources and Sinks in Canada (Environment Canada) Hydraulic fracturing animation (CBC News) The Facts Behind the Frack (Rachel Ehrenberg, ScienceNews) What is fracking and why is it controversial? (BBC)
Chemicals Used in Hydraulic Fracturing (US House of Representatives Committee on Energy and Commerce Minority Staff) Technically Recoverable Shale Oil and Shale Gas Resources: An Assessment of 137 Shale Formations in 41 Countries Outside the United States (US Energy Information Administration)
Ellsworth WL. 2013. Injection-induced earthquakes. Science. 341. http://www.clas.ufl.edu/users/prwaylen/GEO2200%20Readings/Readings/Fracking/Earthquakes%20and%20fracking.pdf Jackson RB et al. 2013. Increased stray gas abundance in a subset of drinking water wells near Marcellus shale gas extraction. Proceedings of the National Academy of Sciences of the USA. 110(28):11250-5 Reins L. 2011. The shale gas extraction process and its impacts on water resources. Review of European Community and International Environmental Law. 20(3):300-312. Solomon S et al. (ed). 2007. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge UK. http://www.ipcc.ch/publications_and_data/ar4/wg1/en/contents.html