Coal seam gas (CSG) extraction results in fugitive methane emissions – a highly flammable and potent greenhouse gas.
These emissions come from:
- leaking pipelines, well heads and processing plants;
- entrained methane in produced water; and
- methane escaping through underground systems.
Very little publicly available research has been undertaken on the carbon footprint of CSG, and therefore its potential to contribute to a reduction in greenhouse emissions and global warming, over its entire life cycle. This information is critical to energy and greenhouse policy.
Research conducted at Cornell University compared the GHG footprint of electricity generated from shale gas, conventional gas, coal and diesel oil over a 20 and 100 year time frame. The researchers estimate that over a 20 year period greenhouse emissions associated with shale gas are 22% to 43% greater than emissions for conventional natural gas. These estimates allow for direct and indirect emissions from electricity production as well as fugitive methane emissions. The researchers found that between 3.6% and 7.9% of methane from shale gas production escapes to the atmosphere in venting and leaks over the lifetime of a well.
Methane has a far greater impact on global warming than previously believed, when the indirect effects of methane on atmospheric aerosols is taken into account. Over 20 years, methane is estimated to have a global warming potential 105 times that of an equivalent amount of carbon dioxide, reducing to 33 times over a 100 year timeframe.
The warming impact of the methane that escapes from the wells, produced water, fittings and pipelines is therefore considerable. Over a 20-year period, leakage of even 1% more than doubles the environmental cost of CSG fired power. The credible leakage figures for CSG start at about 3%.
A study by Atkinson on the hazards of CSG mining in NSW supports this assertion:
‘In September 2004, within a fortnight of the beginning of gas testing, a coal bed methane well north of Newcastle, NSW, was shut down as several boreholes up to 300m away began to blow off methane gas. This was the first reported case of a serious migration of methane gas from coal bed methane operations in New South Wales.’
Atkinson notes that after water is removed from coal seams, methane becomes mobile and can migrate through uncontrolled pathways to the surface, or through nearby openings such as water wells.
The produced water may also contain methane, mostly ‘entrained’ as gas bubbles. Engineers working on CSG technologies in Wyoming have found that the amount lost as entrained gas varies from 2% to 30% of total well yield.