SignificanceOur results demonstrate that access to high-resolution spatiotemporal activity data and multiscale, contemporaneous measurements is critical to understanding oil- and gas-related methane emissions. Careful consideration of all factors influencing methane emissions—including temporal variation—is necessary in scientific and policy discussions to develop effective strategies for mitigating greenhouse gas emissions from natural gas infrastructure.

Divergence in recent oil and gas related methane emission estimates between aircraft studies (basin total for a midday window) and emissions inventories (annualized regional and national statistics) indicate the need for better understanding the experimental design, including temporal and spatial alignment and interpretation of results. Our aircraft-based methane emission estimates in a major U.S. shale gas basin resolved from west to east show (i) similar spatial distributions for 2 days, (ii) strong spatial correlations with reported NG production (R = 0.75) and active gas well pad count (R = 0.81), and (iii) 2× higher emissions in the western half (normalized by gas production) despite relatively homogeneous dry gas and well characteristics. Operator reported hourly activity data show that midday episodic emissions from manual liquid unloadings (a routine operation in this basin and elsewhere) could explain ∼1/3 of the total emissions detected midday by the aircraft and ∼2/3 of the west-east difference in emissions. The 22% emission difference between both days further emphasizes that episodic sources can substantially impact midday methane emissions and that aircraft may detect daily peak emissions rather than daily averages that are generally employed in emissions inventories. While the aircraft approach is valid, quantitative, and independent, our study sheds new light on the interpretation of previous basin scale aircraft studies, and provides an improved mechanistic understanding of oil and gas related methane emissions.

Zimmerle, DJ, et al. 2017 Gathering pipeline methane emissions in Fayetteville shale pipelines and scoping guidelines for future pipeline measurement campaigns. Elem Sci Anth, 5: 70. DOI: https://doi.org/10.1525/elementa.258 Introduction U.S. dry natural gas production increased from 18 to 27 trillion ft 3 between 2005 (EIA, 2016b. Use of natural gas offers potential climate benefits compared to coal or oil (EIA, 2016a), but those benefits depend upon the emissions of methane, the primary component of natural gas and a potent greenhouse gas. This study is part of a larger study designed to compare, and possibly reconcile, estimates of methane emissions developed from aircraft "top-down" measurements (Schwietzke et al., 2017) and inventory-based "bottom up" estimates, including the results presented here and studies of production facilities , gathering compressor stations , and measurements made by downwind techniques (Robertson et al., 2017;Yacovitch et al., 2017) at a variety of facilities.Gathering pipelines refer to the pipelines that connect wells to gathering compressor stations or processing plants, and connect those facilities to transmission pipelines or distribution systems. Inlet pressures of gathering systems range from 30 to 7,720 kPa (Mitchell et al., 2015), but most gathering pipelines operate at the low end of that pressure range. Gathering pipeline systems consist of pipelines and auxiliary components for operation of the pipelines including pig launchers and receivers, blocking valves, and a variety of other, less common, components (e.g. "knock out bottles" used to remove liquids from pipelines on older systems). Pig launchers/receivers are used to insert/remove cleaning plugs, called "pigs", into gathering lines to remove water and debris from the pipeline. Block valves are used to isolate sections of pipeline, or reroute the flow of natural gas (SM-S1).Gathering pipeline network methane emissions originate from three sources: RESEARCH ARTICLEGathering pipeline methane emissions in Fayetteville shale pipelines and scoping guidelines for future pipeline measurement campaigns Gathering pipelines, which transport gas from well pads to downstream processing, are a sector of the natural gas supply chain for which little measured methane emissions data are available. This study performed leak detection and measurement on 96 km of gathering pipeline and the associated 56 pigging facilities and 39 block valves. The study found one underground leak accounting for 83% (4.0 kg CH 4 /hr) of total measured emissions. Methane emissions for the 4684 km of gathering pipeline in the study area were estimated at 402 kg CH 4 /hr [95 to 1065 kg CH 4 /hr, 95% CI], or 1% [0.2% to 2.6%] of all methane emissions measured during a prior aircraft study of the same area. Emissions estimated by this study fall within the uncertainty range of emissions estimated using emission factors from EPA's 2015 Greenhouse Inventory and study activity estimates. While EPA's current inventory is based upon emission factors from distr...

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