What is shale gas, how is it extracted through fracking and what are fracking's impacts?
- What is shale gas and how much is there globally?
Shale gas is a form of natural gas (mostly methane), found underground in shale rock. It is classified as ‘unconventional’ because it is found in shale, a less permeable rock formation than sandstone, siltstone or limestone in which ‘conventional’ gas is found, and it is generally distributed over a much larger area. It does not flow easily.
In 2015, the total amount of unproved technically recoverable reserves of shale gas was estimated at 214.6 trillion cubic metres (tcm), across 46 countries.
The largest estimated resources are in China (31.6 tcm), followed by Argentina (22.7 tcm), Algeria (20 tcm), the United States (17.6 tcm) and Canada (16.2 tcm). In Europe the largest estimated reserves lie in Poland (4.1 tcm) and France (3.9 tcm) (all figures from the US Energy Information Administration).
Shale gas is expected to account for 30 per cent of world natural gas production by 2040.
- How is shale gas extracted through hydraulic fracturing (‘fracking’)?
Hydraulic fracturing – commonly known as fracking – is the process used to extract shale gas. Deep holes are drilled down into the shale rock, followed by horizontal drilling to access more of the gas reserves, as shale reserves are typically distributed horizontally rather than vertically. Fracking fluids containing sand, water and chemicals are then pumped at high pressure into the drilled holes, to open up fractures in the rock, enabling the trapped gas to flow through the fractures into collection wells. From there it is piped away for commercial use. Recovery rates for shale gas are much lower than for conventional gas.
- What are the main environmental impacts of fracking?
In the US, there is some anecdotal evidence of water contaminated by methane due to fracking. In the UK, the risk of water supply contamination is deemed relatively low, given the distance between aquifers and the depth at which fracking occurs. Experts suggest water contamination is more likely to result from spillages on the ground, or cracks in wells allowing leakage – risks faced by all oil and gas extraction – and preventative actions can be taken. Fracking requires relatively large quantities of water and therefore water extraction could have an impact on supplies at a local level.
While shale gas emits lower levels of greenhouse gases when combusted than coal, there are concerns that shale gas extraction could undermine climate change commitments if it replaces the use of renewables. Furthermore, some leakage of methane is possible during shale gas extraction, and so careful monitoring and checks are required.
Other concerns regard local community impacts through the potential noise pollution, increased road traffic (due to lorry movement), damage to the natural environment and space required for drilling sites.
- Can fracking cause earthquakes?
An independent assessment by the Royal Society and the Royal Academy of Engineering in the UK in 2011 concluded that shale gas extraction where large quantities of water are pumped under the surface could in principle cause small earthquakes under certain conditions, but that these were unlikely to lead to damage. The report noted that the risk of seismic activity was greater where pre-stressed faults existed – identified as having occurred at the Preese Hall site in Lancashire, UK – and so recommended ongoing mapping of faults to identify potentially high-risk sites to avoid.