Quantifying alkane emissions in the Eagle Ford Shale using
boundary layer enhancement
Geoffrey Roest and Gunnar Schade
Department of Atmospheric Sciences, Texas A&M University, 3150 TAMU, College Station, Texas 77843-3150
Received: 27 Sep 2016 – Accepted for review: 07 Dec 2016 – Discussion started: 15 Dec 2016
Abstract. The Eagle Ford Shale in southern Texas is home to a booming unconventional oil and gas industry, the climate and air quality impacts of which remain poorly quantified due to uncertain emissions estimates. We used the atmospheric enhancement of alkanes from Texas Commission on Environmental Quality volatile organic compound monitors across the shale, in combination with back trajectory and dispersion modeling, to quantify C2–C4 alkane emissions for a region in southern Texas, including the core of the Eagle Ford, for a set of 68 days from July 2013 to December 2015. Emissions were partitioned into raw natural gas and liquid storage tank sources using gas and headspace composition data, respectively, and observed enhancement ratios. We also estimate methane emissions based on typical ethane-to-methane ratios in gaseous emissions. The median emission rate from raw natural gas sources in the shale, calculated as a percentage of the total produced natural gas in the upwind region, was 0.8 % with an interquartile range (IQR) of 0.5 %–1.4 %, close to the U.S. Environmental Protection Agency's (EPA) current estimates. However, storage tanks contributed 24 % of methane emissions, 54 % of ethane, 82% percent of propane, 90 % of n-Butane, and 83 % of isobutane emissions. The inclusion of liquid storage tank emissions results in an emission rate of 2.2 % (IQR of 0.9 4.9 %) relative to produced natural gas, exceeding the EPA estimate by a factor of two. We conclude that leaks from liquid storage tanks are likely a major source for the observed non-methane hydrocarbon enhancements in the northern hemisphere.
Roest, G. and Schade, G.: Quantifying alkane emissions in the Eagle Ford Shale using
boundary layer enhancement, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-861, in review, 2016.