Field Observations of Methane Emissions from Unconventional and Conventional Fossil Fuel Exploration

Energy from methane (CH₄) has lower carbon dioxide and air pollutant emissions per unit energy produced than coal or oil making it a desirable fossil fuel. Hydraulic fracturing is allowing United States to harvest the nation's abundant domestic shale gas reservoirs to achieve energy independence. However, CH₄ is a gas that is hard to contain during mining, processing, transport and end-use. Therefore fugitive CH₄ leaks occur that are reported in bottom up inventories by the EPA. Recent targeted field observations at selected plays have provided top down CH₄ leak estimates that are larger than the reported EPA inventories. Furthermore, no long-term regional baselines are available to delineate leaks from unconventional mining operations from historical conventional mining. We will report and compare observations of fugitive CH₄ leaks from conventional and unconventional mining to understand changes from technology shifts. We will report in situ and regional column measurements of CH₄, its isotopologue ¹³CH₄ and ethane (C₂H₆) at our Four Corners site near Farmington, NM. The region has substantial coal bed methane, conventional oil and gas production, processing and distribution with minimal hydraulic fracturing activity. We observe large enhancements in in situ and regional column CH₄ with distinct time dependence. Our in situ ¹³CH₄ observations and remote C₂H₆/CH₄ provide strong evidence of thermogenic sources. Comparisons of WRF-simulations with emissions inventory (Edgar) with our observations show that the fugitive CH₄ leaks from conventional mining are 3 times greater than reported. We also compare in situ mobile surveys of fugitive CH₄ and ¹³CH₄ leak signals in basins with conventional (San Juan) mining and unconventional (Permian and Powder River) mining. A large number of active and closed wells were sampled in these regions. Furthermore, play scale surveys on public roads allowed us to gain a regional perspective. The composition of atmospheric ¹³CH₄ observed in the Powder River basin was lighter than the Permian and San Juan basins indicating a higher microbial generated fraction. More extensive and larger CH₄ enhancements were measured in the Permian basin that could be a result of the large expansion of unconventional oil and gas production in this region. However, there are variations amongst wells and plays suggesting that operator practices and reservoir formation play a role in determining the fugitive leaks.