The Greenhouse Gas Impact of Shale Gas Exploitation

Abstract

Shale gas is a hydrocarbon in impermeable shale rock up to 3.5km below the earth surface, requiring hydraulic fracturing, an ‘unconventional’ technique to stimulate production. This study sought to explore the accurate greenhouse gas impact of shale gas exploitation. Emissions from a producing conventional well pad are analogous to an unconventional well pad in production. Methane emissions were measured at three key sites; the KM5 conventional well pad, Knapton generation station and a rural crop farm control site, Cranford Farm. 288 hours of methane measurements were conducted using a Picarro Ring Down Spectrometer, which recorded methane concentration at 1 hertz. A Gull wind sonic was also used to record wind speed and direction. Therefore a flux could be calculated for two natural gas infrastructure sites for comparison. The control site had an average methane concentration of 1.93 ppm, which was higher than the 1.91 ppm CH4 average at the KM5 well pad but lower than that of Knapton which was 2.01 ppm. The average calculated CH4 flux at KM5 was 24.29 kg CH4/year, 3% of the average flux from Knapton, which was calculated as 847.91 kg CH4/year. These annual methane emissions are the equivalent of 3 sheep and 7 dairy cows respectively. Under highest case calculations, methane emissions from these sites equate to emission factors of 0.0077% for KM5 and 0.082% for Knapton. From literature analysis, pre-production emissions from shale gas exploitation will be higher from a) excess energy required for horizontal drilling and hydraulic fracturing and b) methane emissions from well completion. The extent to which it has a larger environmental impact than conventional gas is dependent on the use of REC (reduced emissions completions), which can reduce well completion methane emissions by over 90%. Over longer terms, the Climate Change Act (2008) requires an 80% reduction in GHG emissions from 1990 levels, which will require CCS implementation nationally regardless of shale gas exploitation.