Unaddressed Uncertainties When Scaling Regional Aircraft Emissions Surveys to Basin Emission Estimates

Wide-area aerial methods provide comprehensive screening of methane emissions from oil and gas (O&G) facilities in production basins. Emissions detections (`plumes') from these studies are also frequently scaled to basin level. However, little information exists to determine if plumes detected fugitive emissions or known, reported, maintenance activities. This study analyzed an aircraft field study in the Denver-Julesberg basin to quantify how often plumes identified maintenance events, using a geospatial inventory of 12,629 O&G facilities with facility outlines. Study partners (7 midstream and production operators) provided timing and location of 5910 maintenance events that occurred in a 6-week period. Results indicated three substantial uncertainties with potential bias unaddressed by current prior studies. First, plumes often detect maintenance events, which short-duration, large, and poorly estimated by aircraft methods: 9.2% to 48% [35% to 62%] of plumes on production were likely due to known maintenance events. Second, data indicated that plumes on midstream facilities were both infrequent and unpredictable, calling into question whether these estimates were representative of midstream emissions. Finally, 4 plumes attributed to O&G, representing 19% of all emissions, were not aligned with any location that would logically create emissions. While it is unclear how frequently this occurs, in this study it had material impact on emissions estimates and was detectable only with complete geospatial information. While aircraft emissions detection remains a powerful tool for identifying methane emissions on oil and gas facilities, this study indicates that additional data inputs, such as detailed GIS data, a more nuanced analysis of emission persistence and frequency, and improved sampling strategies are required to accurately scale plume estimates to basin emissions.