Aircraft-Based Estimate of Total Methane Emissions from the Barnett Shale Region

Abstract

We present estimates of regional methane (CH4) emissions from oil and natural gas operations in the Barnett Shale, Texas, using airborne atmospheric measurements. Using a mass balance approach on eight different flight days in March and October 2013, the total CH4 emissions for the region are estimated to be 76 ± 13 × 10(3) kg hr(-1) (equivalent to 0.66 ± 0.11 Tg CH4 yr(-1); 95% confidence interval (CI)). We estimate that 60 ± 11 × 10(3) kg CH4 hr(-1) (95% CI) are emitted by natural gas and oil operations, including production, processing, and distribution in the urban areas of Dallas and Fort Worth. This estimate agrees with the U.S. Environmental Protection Agency (EPA) estimate for nationwide CH4 emissions from the natural gas sector when scaled by natural gas production, but it is higher than emissions reported by the EDGAR inventory or by industry to EPA's Greenhouse Gas Reporting Program. This study is the first to show consistency between mass balance results on so many different days and in two different seasons, enabling better quantification of the related uncertainty. The Barnett is one of the largest production basins in the United States, with 8% of total U.S. natural gas production, and thus, our results represent a crucial step toward determining the greenhouse gas footprint of U.S. onshore natural gas production.

Differences between measured and reported volatile organic compound emissions from oil sands facilities in Alberta, Canada

“…The methodology uses a combination of box-like aircraft flight patterns enclosing each of the main surface mining facilities, comprehensive measurement methods at high time resolution, and the development and application of a computational top-down emission rate retrieval algorithm (TERRA) (25) for deriving facility emission rates from measurements of chemical concentration and meteorology. In contrast to previous aircraft VOC emission studies (26)(27)(28)(29), horizontal and vertical advection and diffusion, chemical reactions, and air mass density changes, all based on measurements, were included in the computation of mass balance of the VOCs from the aircraft measurements, thus reducing the uncertainties in the derived emission rates (25). Another advantage of this methodology is its ability to provide the emission rates of tracers used for the determination of emission rates for many VOCs from discrete measurements, such as canister sampling.…”

Constraining sector-specific CO<sub>2</sub> and CH<sub>4</sub> emissions in the US

“…Despite these omissions, the EPA estimates that 85-90 % of US GHG emissions are covered under the GHGRP. Other recent studies, however, argue that the GHGRP is less complete than estimated by the EPA for two reasons (e.g., Kort et al, 2014;Karion et al, 2015;Lan et al, 2015;Lavoie et al, 2015;Lyon et al, 2015;Mitchell et al, 2015;Subramanian et al, 2015;Zimmerle et al, 2015). First, the emissions that are excluded from the GHGRP are sometimes larger than estimated by the EPA, and second, the EFs used in the GHGRP are smaller than actual emissions from some source sectors like oil and natural gas.…”

“…Furthermore, Brantley et al (2014) explain that these leaks do not correlate with production and can vary greatly in time. Different oil and gas drilling basins also have different overall leakage rates -from 0.3 % in Pennsylvania's Marcellus Shale region to 8.9 % in Utah's Uintah Basin (e.g., Karion et al, 2013Karion et al, , 2015Pétron et al, 2014;Peischl et al, 2015). These factors make it challenging to create consistent, generalizable EFs that can translate activity data into emissions.…”

“…For example, many efforts use a simple box-modeling approach to estimate emissions (e.g., Turnbull et al, 2011;Karion et al, 2013Karion et al, , 2015Caulton et al, 2014;Schneising et al, 2014;Cambaliza et al, 2015;Peischl et al, 2015), while others use an atmospheric transport model to relate GHG observations to emissions (e.g., McKain et al, 2012McKain et al, , 2015. Studies that use the former strategy typically estimate emissions in a few steps: first, they make GHG measurements upwind and downwind of the region of interest.…”

Emissions from oil and gas operations in the United States and their air quality implications

“…Recent field studies have sought to quantify these uncertainties. For example, Allen et al (2015a) assessed differences between observed and inventoried pneumatic controller activity factors and reported a factor of 2-3 difference between observed numbers of pneumatic controllers per well Aircraft-based measurements upwind and downwind of production regions; methane measured using high-precision, high-time-resolution instruments, absorption spectrometry at precise infrared wavelengths; light alkanes analyzed from discrete air samples Emissions (0.48 ± 0.13 Tg/yr) 6.2-11.7% of natural gas production Bottom-up inventories for cattle and gas seepage were subtracted from total emissions; difference assigned to oil and gas activity based on methane to light-alkane ratios Barnett Shale Karion et al, 2015 Aircraft-based measurements upwind and downwind of production regions; methane measured using high-precision, high-time-resolution instruments, absorption spectrometry at precise infrared wavelengths…”