Assessment of methane emissions from the U.S. oil and gas supply chain

“…Although we do not calculate the FA&D-associated emissions, Mann et al report that the FA&D stage contributes to the CHPs’ lifecycle GHG (< 20%), CO (> 60%), NO X (> 80%), and VOC (∼20%) emissions, assuming a CH 4 leakage rate of 1.4 ± 0.5% of the gross NG produced. Because this leakage rate may be underestimated, , the contributions of FA&D toward the overall emissions may be higher.…”

“…Our finding that average anthropogenic FF emissions for 2003-2012 are similar to bottom-up estimates may appear to conflict with recent studies showing underestimated fugitive CH 4 emissions from oil and gas production regions (Alvarez et al, 2018), flaring sites (Plant et al, 2022), some urban regions (Sargent et al, 2021), and some unexpected CH 4 "superemitters" (Lauvaux et al, 2022). To reconcile these findings, it could be that underestimated fugitive emissions are not globally significant (given our uncertainty of 24 Tg CH 4 yr 1 , defined as the difference between the 84th percentile and mean), as suggested by a recent high-resolution inversion study (Shen et al, 2023), or that some other FF sources are overestimated in bottom-up inventories.…”

“…From the CH 4 -C 2 H 6 joint optimization, we estimate O&G emissions from the South Central United States to be 1.8x ± 0.7 higher than 2012 EPA inventory estimates. This result is in agreement with national-scale aggregated estimates derived in Alvarez et al (2018) (1.5-1.9x) and Omara et al (2018) (1.5-3.3x, production sector only), as well as numerous top-down estimates of individual basins which have measured emissions higher than inventory estimates (Brandt et al, 2014). For top-down studies, there have been concerns that these estimates may contain bias due to their reliance of daytime measurements, unable to account for potential diurnal differences in O&G emissions that could exist due to different levels of onsite maintenance and activity (Vaughn et al, 2018).…”