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Methane emissions undermine switch from coal to gas

  • 07 Jan 2013, 17:00
  • Mat Hope

Source: Baracoda

Questions are being asked about the emissions benefits of shale gas after new research shows high levels of methane emissions leaking from two gas fields in the United States.

Natural gas has about half the carbon emissions of coal when it is burnt, so burning gas instead of coal can significantly lower emissions. But there would be less benefit in switching to gas if significant amounts of greenhouse gases like methane leak into the atmosphere when gas is extracted from unconventional sources like shale.

Fugitive emissions

The process of extracting shale gas is not perfect. Not all the gas released from shale rock formations is captured, and some leaks out - so-called fugitive emissions.

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, or fracking. A significant portion of the water returns to the surface accompanied by large quantities of the greenhouse gas methane, which flows naturally into boreholes and is collected at wells. Some methane, however, escapes into the atmosphere while the wells are being built, and this makes up the majority of fugitive emissions.

Alarming emissions

Research from the Environmental Defense Fund and Princeton University suggests that for there to be significant climatic benefits of switching to gas from coal, as the US is doing, the amount of methane that leaks into the atmosphere from all natural-gas sources needs to be less than 3.2 per cent.

The new research from the National Oceanic and Atmospheric Administration (NOAA) and the University of Colorado in Boulder found that nine per cent of the methane produced from two fields in Utah and Colorado was leaking out.

If methane is leaking from other fields at a similar rate then the apparent emissions benefit of switching to gas is lost, and so nailing down exactly how much gas escapes in general is important to take into account when making choices about the amount of gas to include the energy mix.

Uncertain emissions and energy choices

While the study adds to the body of information on fugitive emissions, the larger picture is still unclear - and contested.

A study by Cornell University in 2011 concluded that fugitive emissions meant that shale gas would be even more polluting than coal, but that study has come under a great deal of criticism by people who question its methodology. The authors of the Cornell study have disagreed with the criticisms of their paper, suggesting that four per cent of the methane produced in the fields they examined was leaking.

It remains difficult to know the precise level of fugitive emissions and how it would affect choices about the role of gas in the energy mix.

There is a lot riding on getting better information about fugitive emissions. If the fugitive emissions from fracking were generally as high as the NOAA research indicates, it would presumably undermine the benefits of the US switching from coal to gas - as far as emissions go, at least.

 

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