The lead research institutions, with contractors and industry participants, conducted a series of studies that dealt with various aspects of the methane emissions reconciliation problem. The entirety of the efforts culminated in a CSU-led capstone paper that ties together measurement results from all methods used.
Individual studies that comprise the Basin Methane Reconciliation Study include the following:
Capstone Paper | Summary Paper | Aircraft Methods and Results | Methods comparison 1 – Production | Methods comparison 2 – Gathering | Multi-Basin comparison 1 | Multi-Basin comparison 2 | Pipeline Methods and Results | Attribution
This paper compares the bottom-up model to the top-down measurements made during the study. The paper describes details of the bottom-up model, including spatial and temporal aspects of the model, and the comparison to the top-down measurements. Sensitivity studies illustrate how variations in emissions data or emissions timing could be used to further reduce differences between top-down and bottom-up measurements in the future. For more information, see the frequently asked questions.
Vaughn TL, Bell CS, Pickering CK, Schwietzke S, Heath GA, Pétron G, Zimmerle D, Schnell RC, Nummedal D. 2018 Oct 29. Temporal Variability Largely Explains Difference in Top-down and Bottom-up Estimates of Methane Emissions from a Natural Gas Production Region. Proc Natl Acad Sci. doi: 10.1073/pnas.1805687115
Aircraft Methods and Results
This paper quantifies midday methane emissions from all sources in the Fayetteville Shale study area using aircraft-based high resolution methane and wind measurements on two consecutive days. It is the first paper to use the aircraft mass-balance technique to derive spatially resolved, top-down methane emission estimates for a natural gas play while also improving the calculation method. Natural gas related methane emissions (normalized by gas production) in the western half were found to be double that in the eastern half. Episodic maintenance emissions from manual liquid unloadings at a small fraction of producing well pads could explain about one-third of the total emissions detected midday by the aircraft and about two-thirds of the west−east difference in emissions. (Schwietzke et al., 2017)
Reference: Schwietzke S, Pétron G, Conley S, Pickering C, Mielke-Maday I, Dlugokencky EJ, Tans PP, Vaughn T, Bell C, Zimmerle D, et al. 2017 May 26. Improved Mechanistic Understanding of Natural Gas Methane Emissions from Spatially Resolved Aircraft Measurements. Environ Sci Technol 51 (12), 7286–7294. doi: 10.1021/acs.est.7b01810
Methods comparison 1 – Production
This paper compares multiple methane measurements (onsite, OTM33a and tracer) used at production facilities during the study, focusing on comparisons of when these methods were applied concurrently. A study onsite estimate is developed from direct measurements made by the onsite team plus simulated sources which were not measured by the onsite team. Manual liquids unloading emissions contribute to the overwhelming majority of the methane emissions from production sites in the study area. The paper shows the tracer and study onsite estimate agree at 15 of 16 paired facilities, while OTM and study onsite estimate agree at only 22 of 43 paired facilities. Linear regressions show OTM33a tends to estimate lower emissions relative to the onsite technique, while tracer tends to estimate higher emissions than the onsite technique. (Bell et al., 2017)
Reference: Bell C, Vaughn T, Zimmerle D, Herndon S, Yacovitch T, Heath G, Pétron G, Edie R, Field R, Murphy S, et al. 2017. Comparison of methane emission estimates from multiple measurement techniques at natural gas production pads. Elem Sci Anth 5(0). doi: 10.1525/elementa.266
Methods comparison 2 – Gathering
This paper uses multiple methods (onsite and tracer) to measure methane emissions at production facilities during the study. The results indicate that uncombusted methane emissions contribute to the majority of the methane emissions at gathering facilities. Tracer estimates show lower emissions at gathering facilities than the onsite estimate. (Vaughn et al., 2017)
Reference: Vaughn TL, Bell CS, Yacovitch TI, Roscioli JR, Herndon SC, Conley S, Schwietzke S, Heath GA, Pétron G, Zimmerle D. 2017. Comparing facility-level methane emission rate estimates at natural gas gathering and boosting stations. Elem Sci Anth 5(0). doi: 10.1525/elementa.257
Multi-Basin comparison 1
This paper looks at differences in emissions at natural gas production sites for four basins, including that of the Fayetteville Shale Play, employing the OTM 33A method. The study compares absolute emissions and throughput-weighted emissions. (Robertson et al., 2017)
Reference: Robertson AM, Edie R, Snare D, Soltis J, Field RA, Burkhart MD, Bell CS, Zimmerle D, Murphy SM. 2017 Jun 19. Variation in Methane Emission Rates from Well Pads in Four Oil and Gas Basins with Contrasting Production Volumes and Compositions. Environ Sci Technol, in press. doi: 10.1021/acs.est.7b00571
Multi-Basin comparison 2
This paper looks at methane emissions from production and gathering facilities measured in the Fayetteville (FV) Shale study area in Arkansas, and the Denver-Julesburg basin in Colorado utilizing dual-tracer methods. These measurements are compared with distributions from multi-basin national measurements. When scaled by throughput, FV gathering station emissions are lower than the multi-basin results. (Yacovitch et al., 2017)
Reference: Yacovitch TI, Daube C, Vaughn TL, Bell CS, Roscioli JR, Knighton WB, Nelson DD, Zimmerle D, Pétron G, Herndon SC. 2017. Natural gas facility methane emissions: measurements by tracer flux ratio in two US natural gas producing basins. Elem Sci Anth 5(0). doi: 10.1525/elementa.251
Pipeline Methods and Results
This paper discusses gathering line measurements from the field campaign and the modeling of rare emission events, since there are few leaks during pipeline surveys. It further suggests a design for future measurement campaigns to improve uncertainty around emission estimates from pipeline leaks. (Zimmerle et al., 2017)
Reference: Zimmerle DJ, Pickering CK, Bell CS, Heath GA, Nummedal D, Pétron G, Vaughn TL. 2017. Gathering pipeline methane emissions in Fayetteville shale pipelines and scoping guidelines for future pipeline measurement campaigns. Elem Sci Anth 5(0). doi: 10.1525/elementa.258
This paper attempts to quantify a portion of total methane emissions that result from natural gas operations in the study area using ethane-to-methane enhancement ratios derived from mobile ground and airborne calibrated trace gas measurements. The top-down attribution showed that on average 90 percent of methane emissions in the Western half of the FV study area were attributable to natural gas operations. Lower emissions and lower atmospheric enhancements over the eastern half did not support a quantitative top-down attribution.
Reference: Mielke-Maday I, Schwietzke S, Thorley E, Yacovitch TI, Herndon SC, Conley S, Kofler J, Handley P, Miller B, Hall B, Dlugokencky E, Lang P, Wolter S, Moglia E, Crotwell M, Crotwell A, Rhodes M, Kitzis D, Vaughn T, Bell C, Zimmerle D, Schnell R, Pétron G. Methane source attribution in a U.S. dry gas basin using spatial patterns of ground and airborne ethane and methane measurements.
Manuscript submitted for publication.