Natural gas is typically considered to be the cleaner-burning fossil fuel that could play an important role within a restricted carbon budget. Whilst natural gas emits less CO2 when burned than other fossil fuels, its main constituent is methane, which has a much stronger climate forcing impact than CO2 in the short-term. Estimates of methane emissions in the natural gas supply chain are subject to much controversy, due to uncertainties associated with estimation methods, data quality and assumptions used. This paper presents a comprehensive analysis of estimated CO2 and methane emissions across the global natural gas supply chain, with the aim of providing a balanced insight for academia, industry and policy makers by summarising the agreed upon data, locating the contentious issues and identifying where further work is needed to reduce or remove this contention. Overall, the range of documented estimates of methane emissions across the supply chain is vast amongst an aggregation of different geological formations, technologies, plant age, gas composition and regional regulation, not to mention differences in estimation methods. Estimates of combined methane and CO2 emissions ranged from 2 – 42 g CO2 eq./ MJ HHV, whilst methane-only emissions ranged from 0.2% – 10% of produced methane. The methane emissions at the extraction stage are the most contentious issue, with limited data available but potentially large impacts associated with well completions for unconventional gas, liquids unloading and also from the transmission stage. However, various new technologies, mitigation approaches, and legislation are driving significant reductions in methane leakage across the natural gas supply chain. The presence of ‘super emitter’ facilities, a small number of facilities that cause extremely high emissions, is found across all supply chain stages creating a highly skewed emissions distribution. This paper has created a definitive baseline for further work and provided clarity for industry, policy makers and academia on the range of emissions and causes of such a range.
Paul is currently a research associate at the Sustainable Gas Institute, investigating the environmental and economic impacts associated with the natural gas supply chain and determining pathways to reduce these impacts.