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Carbon Brief Staff

29.05.2012 | 2:00pm
ScienceFugitive emissions from shale gas: our Q&A
SCIENCE | May 29. 2012. 14:00
Fugitive emissions from shale gas: our Q&A

A report released today by the International Energy Agency suggests a series of Golden Rules for a Golden Age of Gas. One of the proposed rules is that the question of ‘fugitive emissions’ from shale gas extraction is addressed. The IEA writes:  

“Greenhouse-gas emissions must be minimised both at the point of production and throughout the entire natural gas supply chain. Improperly addressed, these concerns threaten to curb, if not halt, the development of unconventional resources.”

The question of fugitive emissions – how significant they are, and what they mean for the extraction of shale gas in the UK and elsewhere, remains remains highly contested. In the Q&A below, we have laid out the state of play as we understand it.

What are fugitive emissions?

The process of extracting shale gas, also known as fracking, is not perfect at the moment. Not all the gas released from shale rock formations is captured, so some leaks out.  

Gas also leaks during the refining process and when transporting the end product to our homes, from example from damaged or poorly maintained pipes – although this doesn’t just apply to shale gas but to conventional gas as well. According to one paper, leaks from the Russian long distance natural gas pipeline network account for 0.6 per cent of the natural gas transported.

In both cases, these accidental leaks are known as fugitive emissions.

How does it happen?

When shale gas is extracted, large volumes of pressurised water  – along with small amounts of sand and chemicals – are forced into shale formations deep underground in a process called hydraulic fracturing, which has become known as “fracking”.

A significant portion of the water returns to the surface accompanied by large quantities of methane, which flows naturally into boreholes and is collected at wells. Some methane, however, escapes into the atmosphere during well completion. This makes up the majority of so-called fugitive emissions, even taking into account leakage that occurs when the gas is being transported.

How big a problem is it?

Methane is a greenhouse gas, which, although short-lived in the atmosphere relative to carbon dioxide, is approximately 25 times more powerful over a 100 year timescale. So leakage of methane directly into the atmosphere isn’t a good idea if you want to keep greenhouse gas emissions down.

The problem is that we don’t really know how much methane leaks out during the fracking process and researchers currently don’t agree on the figures.

It’s important that we get a clearer idea because more and more countries are exploring the potential for indigenous production of unconventional gas, which has really taken off in the US. It looks like we could see the same happening elsewhere as reserves of shale have been identified in Europe, China and Russia – although it looks like this will be easier in some countries than others, depending on their geography and legal frameworks.

What does the data show so far?

A 2011 study by Cornell University (Cornell study 2011) concluded that fugitive emissions mean that shale gas would be even more environmentally polluting than coal. The study has come under a great deal of criticism (Cathles et al, 2011), however, by people who question its methodology.

Other studies including a literature survey by the Manchester Tyndall Centre and two different papers in Environmental Research Letters indicate that emissions from shale gas are only slightly higher than conventional gas – much less than the amount given by the Cornell researchers.

But the authors of the Cornell study have disagreed with the criticisms (Howarth et al, 2012) of their paper – and the early bits of hard data on methane emissions from the process appear to back them up.

That’s not the end of the disagreement either – the group critical of the original Cornell University study has recently published a paper in the Geochemistry, Geophysics, Geosystems journal, which insists that replacing coal with gas power plant is still an efficient method of reducing emissions and tackling climate change.

Our graphic below compares different researchers’ assessments of fugitive emissions as a percent of the total emissions from both conventional gas and shale gas wells. It shows just how much disagreement there is between scientists on the subject:

Shale _gas _graphic

EPA figures calculated by Howarth et al 2012.
Fugitive emissions expressed as percentage of total emissions over the lifecycle of the well.Source: Methane Emissions from Natural Gas Systems (2012)

Who is claiming what?

The disagreement amongst researchers gives everyone an opportunity to cite figures that appear to support their case. ExxonMobil’s vice president of public and government affairs Ken Cohen, for example, prefers the lower estimates – but then Exxon has bet high on the US shale gas revolution. Energy In Depth, the industry-backed group that supports shale gas exploration in the US, has also been keen to discredit the first Cornell study.

In contrast, environmentalists like Tony Juniper have cited the higher figures from the 2011 Cornell study in support of the contention that shale gas is “comparable to coal” in terms of emissions. Research from the Canadian site DeSmogBlog, which opposes fracking, also cites the higher figures to argue that shale gas isn’t as clean as many suggest. The US Environmental Protection Agency acknowledges that previous estimates it made about overall fracking emissions could have underestimated the real figures.

Where do we go from here?

Initial drilling by Cuadrilla was found to be ” highly probably” responsible for two minor earthquakes near Blackpool last year. Cuadrilla have since suspended their drilling in the area.

A report released in April of this year concluded that “DECC see no need for any moratorium on shale gas.”  The  DECC consultation on the report ended last Friday, and according to  media reports the government is likely to give the go-ahead to fracking in the next few weeks.

So where does that leave us? The question of how much fugitive emissions really do add to the impact of shale gas on climate change remains essentially unanswered. Should the UK proceed with a major expansion of production from shale gas, the consequent impact on our emissions also remains an unknown quantity until further research is carried out.

UPDATE 5pm 29th May: The section on the suspension of fracking by Cuadrilla was altered in response to the first comment below.

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