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Robin Webster

22.04.2014 | 1:30pm
EmissionsStudy: “plumes” of methane released into the atmosphere by a few super-emitting shale gas wells
EMISSIONS | April 22. 2014. 13:30
Study: “plumes” of methane released into the atmosphere by a few super-emitting shale gas wells

Methane emissions from some shale gas wells could be up to a thousand times higher than official estimates – meaning they have a warming effect orders of magnitude higher than previously thought. But the finding only refers to a few ‘super-emitter’ sites, a tiny proportion of the total number of drilling locations, according to a recent study.

The government argues that the UK could burn gas instead of coal as a way of cutting greenhouse gas emissions from the energy system. That includes domestically produced shale gas.

But some academics argue that gas leaks during the process of extracting shale gas from rock – known as fracking – could make the fuel far more climate-polluting than its supporters claim.

The evidence is contested, and other researchers disagree. But a new study from researchers at a number of American universities appears to support the idea that ‘fugitive’ or unplanned emissions from shale gas wells could be substantial. The study identifies a small number of sites where drilling for shale gas has released large amounts of methane into the atmosphere.

A methane puzzle 

Natural gas releases about half the carbon emissions that coal does when burnt, so it’s generally viewed as a much less carbon-intensive fuel.

But how much less depends on how much gas leakage occurs during production. Natural gas is mainly methane, a powerful greenhouse gas. When it escapes into the atmosphere, it adds to the warming effect of climate change.

There’s a lot more methane in the atmosphere in the moment than there should be – presenting researchers with a puzzle as to where it’s coming from. Could natural gas operations be releasing more gas into the atmosphere than previously believed?

Methane plumes

In order to answer the question, researchers from Purdue University and the University of California went up in a specially equipped aeroplane to measure methane levels in the atmosphere above shale gas drilling sites.

Out of the many shale gas wells in the area it assessed in south-west Pennsylvania, some appeared to be releasing anomalously high levels of methane. In two areas, researchers observed “multiple high concentration methane plumes”. Zoning in on the areas, they identified seven well pads releasing very high levels of methane.

These shale gas wells – where companies were still drilling for the gas, and not yet extracting it – were releasing 100 to 1,000 times more methane into the atmosphere than official estimates suggest, the researchers concluded.

A few super-emitter sites

These results lend support to another recent study, which concluded that natural gas operations are leaking more gas than officially recognised – but that just a few so-called ‘super-emitter’ sites are largely responsible.

In the latest study, just one per cent of sites – seven well pads, or about 40 shale gas wells – accounted for somewhere between four and 30 per cent of the methane emissions the researchers measured.

The researchers suggest “underbalanced drilling methods” may be responsible at the sites in question. This is where lower pressure in the well allows fluids and gas from the various geological formations – for example coal deposits – to seep out during the drilling phase, and ultimately escape into the atmosphere.

The difficulties of scaling up

Evidence from elsewhere in the USA means this may be a national-level problem rather than just a local one, the study suggests.

But it’s hard to draw conclusions too broadly. This study only addresses the drilling stage of shale gas extraction – rather than other stages in the process like extraction, processing or transportation. As one of the study’s co-authors, Professor Paul Shepson, tells Carbon Brief:

“The drilling phase typically lasts about two weeks.  And it is one component of the system.  And, we observed seven well pads out of hundreds in the Marcellus [shale rock], over a period of two days.”

Shipson adds that it would be “dangerous” to scale the result up to other regions, or to make assumptions about what this might mean for conventional gas extraction rather than shale gas. The gas emissions observed here may occur as a result of the particular geochemistry of this region, which may not apply elsewhere.

In one sense, the results may be good news for advocates of gas as a low-carbon fuel – because they suggest that just a few sites may be responsible for a significant portion of ‘fugitive’ methane emissions, which should make the issue easier to address.

But they also show that in a few locations, it’s possible for significant methane leaks to occur without anyone knowing about it – making those operations far more climate-polluting than previously assumed.

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