Methane Destruction Efficiency of Natural Gas Flares Associated with Shale Formation Wells

Flaring to dispose of natural gas has increased in the United States and is typically assumed to be 98% efficient, accounting for both incomplete combustion and venting during unintentional flame termination. However, no in situ measurements of flare emissions have been reported. We used an aircraft platform to sample 10 flares in North Dakota and 1 flare in Pennsylvania, measuring CO₂, CH₄, and meteorological data. Destruction removal efficiency (DRE) was calculated by assuming a flare natural gas input composition of 60–100% CH₄. In all cases flares were >99.80 efficient at the 25% quartile. Crosswinds up to 15 m/s were observed, but did not significantly adversely affect efficiency. During analysis unidentified peaks of CH₄, most likely from unknown venting practices, appeared much larger in magnitude than emissions from flaring practices. Our analysis suggests 98% efficiency for nonsputtering flares is a conservative estimate for incomplete combustion and that the unidentified venting is a greater contributor to CH₄ emissions

Aircraft-Based Measurements of Point Source Methane Emissions in the Barnett Shale Basin

We report measurements of methane (CH₄) emission rates observed at eight different high-emitting point sources in the Barnett Shale, Texas, using aircraft-based methods performed as part of the Barnett Coordinated Campaign. We quantified CH₄ emission rates from four gas processing plants, one compressor station, and three landfills during five flights conducted in October 2013. Results are compared to other aircraft- and surface-based measurements of the same facilities, and to estimates based on a national study of gathering and processing facilities emissions and 2013 annual average emissions reported to the U.S. EPA Greenhouse Gas Reporting Program (GHGRP). For the eight sources, CH₄ emission measurements from the aircraft-based mass balance approach were a factor of 3.2–5.8 greater than the GHGRP-based estimates. Summed emissions totaled 7022 ± 2000 kg hr^–1, roughly 9% of the entire basin-wide CH₄ emissions estimated from regional mass balance flights during the campaign. Emission measurements from five natural gas management facilities were 1.2–4.6 times larger than emissions based on the national study. Results from this study were used to represent “super-emitters” in a newly formulated Barnett Shale Inventory, demonstrating the importance of targeted sampling of “super-emitters” that may be missed by random sampling of a subset of the total