Development of a national estimate of methane emissions from United States natural gas gathering facilities and processing plants

Abstract:

New facility-level methane emissions measurements obtained from 114 natural gas gathering facilities and 16 processing plants in 13 U.S. states were combined with facility counts obtained from state and national databases in a Monte Carlo simulation to estimate methane emissions from U.S. natural gas gathering and processing operations. Total annual methane emissions of 2,421 (+245/-237) Gg were estimated for all U.S. gathering and processing operations, representing a methane loss rate of 0.47% (±0.05%) when normalized by 2012 CH₄ production. The largest source of emissions from gathering and processing operations were attributed to normal operation of gathering facilities (1,697 +189/-185 Gg). The methane emissions from processing plants (506 +55/-52 Gg) was 40% lower than the 2014 EPA Greenhouse Gas Inventory (GHGI) estimate but a factor of three higher than that reported under the EPA Greenhouse Gas Reporting Program. Since gathering operations are currently embedded within the production segment of the EPA GHGI, field observations equipment counts at gathering facilities were used to estimate the fraction of the methane emissions in the EPA production inventory to assign to gathering facilities. Based on this analysis, the study results suggest that methane emissions from gathering facilities could be as high as eight times that of the EPA GHGI estimate. Because methane emissions from most gathering facilities are not reported under the current rule and not all source categories are reported for processing plants, the total CH₄ emissions from gathering and processing reported under the EPA GHGRP (180 Gg) represents only 14% of that tabulated in the EPA GHGI and 7% of that predicted from this study.