Methane Emissions from Natural Gas Production Sites in the United States: Data Synthesis and National Estimate

We
used site-level methane (CH4) emissions data from
over 1000 natural gas (NG) production sites in eight basins, including
92 new site-level CH4 measurements in the Uinta, northeastern
Marcellus, and Denver-Julesburg basins, to investigate CH4 emissions characteristics and develop a new national CH4 emission estimate for the NG production sector. The distribution
of site-level emissions is highly skewed, with the top 5% of sites
accounting for 50% of cumulative emissions. High emitting sites are
predominantly also high producing (>10 Mcfd). However, low NG production
sites emit a larger fraction of their CH4 production. When
combined with activity data, we predict that this creates substantial
variability in the basin-level CH4 emissions which, as
a fraction of basin-level CH4 production, range from 0.90%
for the Appalachian and Greater Green River to >4.5% in the San
Juan
and San Joaquin. This suggests that much of the basin-level differences
in production-normalized CH4 emissions reported by
aircraft studies can be explained by differences in site size and
distribution of site-level production rates. We estimate that NG production
sites emit total CH4 emissions of 830 Mg/h (95% CI: 530–1200),
63% of which come from the sites producing <100 Mcfd that account
for only 10% of total NG production. Our total CH4 emissions
estimate is 2.3 times higher than the U.S. Environmental Protection
Agency’s estimate and likely attributable to the disproportionate
influence of high emitting sites.