Footnotes: Supporting annex on analytical assumptions
1 P90, P50 and P10 are the estimates provided with the relevant percentage level of confidence. For example, the P90 value is an estimate made with 90% confidence.
4 The reason for the poor performance of the wells is thought to be due to the presence of loam (clay) in the shale; on contact with water the loam swells reducing the gas flow.
IDDRI (2014) Unconventional Wisdom,
Available at: http://www.iddri.org/Publications/Unconventional-wisdom-economic-analysis-of-US-shale-gas-and-implications-for-the-EU
7 It should be noted that the economic life of the well is likely to be shorter than the productive life; therefore the total volume of gas produced from the well is likely to be smaller than the EUR.
Methane and CO
2 emissions from the natural gas supply chain,
9 Bond et al. (2014), Life-cycle Assessment of Greenhouse Gas
Emissions from Unconventional Gas in Scotland,
10 The highest in literature is 6,800,000 m3 as estimated by Howarth.
11 Marchese et al. (2015) Methane Emissions from United States
Natural Gas Gathering and Processing.
12 Allen et al. (2013) Measurements of methane emissions at
natural gas production sites in the United States. Proc. Natl.
Acad. Sci. U. S. A. 2013, 110 (44), 17768−17773.
13 Brantley et al. (2014) Assessment of Methane Emissions from
Oil and Gas Production Pads using Mobile Measurements.
14 We assume the average economic life of a well at 20 years.
15 In reality we expect the emission associated with each subsequent workover to be lower due to a drop in well productivity and reservoir pressure.
Recommended Technologies to Reduce Methane Emissions,
17 This well had 7,500 unloading events per year. It is unlikely that this number of events would be replicable without an automated plunger lift system.
18 We assume that the potential for 'super-emissions' increases as the equipment ages.