Multi-scale Methane Measurements at Oil and Gas Facilities Reveal Necessary Framework for Improved Emissions Accounting

Abstract

Methane mitigation from the oil and gas (O&G) sector represents a key near-term global climate action opportunity. Recent legislation in the United States requires updating of current methane reporting programs for oil and gas facilities with empirical data. While technological advances had led to improvements in methane emissions measurements and monitoring, the overall effectiveness of mitigation strategies rests on quantifying spatially and temporally varying methane emissions more accurately than current approaches. In this work, we demonstrate a quantification, monitoring, reporting, and verification framework that pairs snapshot measurements with continuous emissions monitoring systems (CEMS) to reconcile measurements with inventory estimates and account for intermittent emissions events. We find site-level emissions exhibit significant intra-day and daily emissions variation. Snapshot measurements of methane can span over three orders of magnitude and may have limited application in developing annualized inventory estimates at site-level. Consequently, while official inventories underestimate methane emissions on average, emissions at individual facilities can be higher or lower than inventory estimates. Using CEMS, we characterize distributions of frequency and duration of intermittent emission events. Technologies that allow high sampling frequency such as CEMS, paired with a mechanistic understanding of facility-level events, are key to accurate accounting of short-duration, episodic, and high-volume events that are often missed in snapshot surveys, and to scale snapshot measurements to annualized emissions estimates.

Impact of the High-Emission Event Duration and Sampling Frequency on the Uncertainty in Emission Estimates

“…12 Cusworth et al, 11 sampling a larger number of sites, found that short-lived (<1 month) and long-lived (>1 year) sources were both significant contributors to overall emissions across multimonth and multiyear campaigns. Wang et al also found that for some oil and gas basins, the most common emission duration was <1 h. 13 The variability in emission magnitude and duration requires that a large number of observations be taken to accurately measure and represent these high-emission events.…”