Projecting the Temporal Evolution of Methane Emissions from Oil and Gas Production Sites

Abstract

Many recent studies have reported methane emissions from oil and gas production regions, often reporting results as a methane emission intensity (methane emitted as a percentage of natural gas produced or methane produced). Almost all of these studies have been instantaneous snapshots of methane emissions; however, total methane emissions from a production site and the methane emission intensity would be expected to evolve over time. A detailed site-level methane emission estimation model is used to estimate the temporal evolution of methane emissions and the methane emission intensity for a variety of well configurations with and without emission mitigation measures in place. The general pattern predicted is that total emissions decrease over time as production declines. Methane emission intensity shows complex behavior because production-dependent emissions decline at different rates and some emissions do not decline over time. Prototypical uncontrolled wet gas wells can have approximately half of their emissions over a 10 year period occur in the first year; instantaneous wellsite methane emission intensities range over a factor of 3 (0.62–2.00%) in the same period, with a 10 year production weighted-average lifecycle methane emission intensity of 0.79%. Including emission control in the form of a flare can decrease the average lifecycle methane emission intensity to 0.23%. Emissions from liquid unloadings, which are observed in subsets of wells, can increase the lifecycle methane emission intensity by up to a factor of 2–3, between 1.2 and 2.3%, depending on the characteristics of the unloadings. Emissions from well completion flowbacks raise the average lifecycle methane emission intensity from 0.79 to 0.81% for flowbacks with emission controls; for flowbacks with uncontrolled emissions, lifecycle methane emissions increase to 1.26%. Dry gas and oil wells show qualitatively similar temporal behavior but different absolute emission rates.

New Technologies can Cost-effectively Reduce Oil and Gas Methane Emissions, but Policies will Require Careful Design to Establish Mitigation Equivalence

“…The sensitivity analysis presented in SI section S4 suggests that improving precision in the leak production rate estimate will decrease uncertainty the most, followed by developing basinspecific emission distributions. Coupling FEAST with a process-based model similar to that described by Cardoso-Saldon et al [39] would provide a more accurate model of vents and further reduce uncertainty. We draw the following broad conclusions from the results of this work that can aid oil and gas operators and regulatory agencies in developing LDAR programs using new methane detection technologies:…”

Large-Scale Controlled Experiment Demonstrates Effectiveness of Methane Leak Detection and Repair Programs at Oil and Gas Facilities

“…Sites that do not have any "repaired" tags throughout surveys are grouped under "Not Repaired". Based on these definitions, there are 54 sites that underwent repairs at least once, including 26…”

“…Most field studies of methane emissions from oil and gas facilities using new technologies such as aircraft and satellite provide 'snap-shot' measurement data -while detailed in spatial extent, they do not shed light on temporal variations in emissions [12], [26]. This is critical as recent measurements have observed significant differences in emissions across seasons, time of day, and other temporal variables [27], [28].…”

Meteorological Drivers of Permian Basin Methane Anomalies Derived from TROPOMI

“…Several interesting spatial patterns have emerged in the average variability of CH 4 columns cross the Permian Basin between 1 December 2018 and 1 December 2020 ( Figure 3). In the next two subsections, the impacts of meteorological transport for four case study periods-two with frequent westerly winds (8-15 March 2019 and 1 April-10 May 2019, referred to as the "windy" cases) and two dominated by high pressure and low wind speeds (16)(17)(18)(19)(20)(21)(22)(23) March 2019 and 24 September-9 October 2020, referred to as the "quiescent" cases)-are presented.…”

“…As a greenhouse gas, CH 4 is more potent than carbon dioxide (CO 2 ), such that, as CH 4 emissions increase through ONG production, its positive benefits as a cleaner burning fuel can be overshadowed by its climate forcing [11,12]. Consequently, there has been considerable research on improving understanding of highly variable emissions of CH 4 and other trace gases from ONG production regions [13][14][15][16][17][18].…”