Monitoring Methane Emissions from Oil and Gas Operations^‡

The atmospheric concentration of methane has more than doubled since the start of the Industrial Revolution. Methane is the second-most-abundant greenhouse gas created by human activities and a major driver of climate change. This APS-Optica report provides a technical assessment of the current state of monitoring U.S. methane emissions from oil and gas operations, which accounts for roughly 30% of U.S. anthropogenic methane emissions. The report identifies current technological and policy gaps and makes recommendations for the federal government in three key areas: methane emissions detection, reliable and systematized data and models to support mitigation measures, and effective regulation.

Popular Summary

Methane is both a fossil fuel and a potent greenhouse gas, with a much stronger impact on global warming than an equivalent mass of carbon dioxide. It is released into our atmosphere through agriculture, waste decomposition, and the extraction and processing of fossil fuels. This policy report details the accidental release of methane during fossil fuel production, a first step in much of the energy generation in the world today. Finding and addressing large methane leaks from super-emitters in the fossil-fuel sector could significantly reduce the atmospheric concentration of this greenhouse gas. The authors of the report outline specific, actionable goals for both physics and optics researchers and policymakers in federal agencies to address this problem. Scientific research into methane detection modeling and technology can drive the development of scalable, user-friendly leak monitoring systems. These advances in detection should, according to the authors, be supported by government initiatives to create robust policies for identifying and combating leaks from super-emitters.

Figure 1

Monthly flare volumes for two representative sites in the Permian Basin for the three-year period from February 2018 to February 2021, as reported by satellite observations (blue triangles) [16, 17, 18] and by the state regulator based on self-reported data from the operator to the state regulating agency (red circles). The overall averages are marked with solid horizontal lines, using the same color code. For the right-hand site, the overall satellite flare volume is nearly twice the operator-reported volume, while the reverse is true for the left-hand site. The dashed lines are guides to the eye. There is considerable scatter in the data, and it would be helpful to have a finer mesh to explore the relationship of the relative measurements.

Figure 2

The top 10 countries by satellite-retrieved volume of flared gas, 2012–2020. The World Bank [19] reports that Russia, Iraq, Iran, the United States, Algeria, Venezuela, and Nigeria remain the top seven gas-flaring countries for nine years running. These seven countries produce 40% of the world’s oil each year, but account for 65% of global gas flaring.

Figure 3

Component and facility emissions and measurement detection threshold. Magnitude of oilfield methane emissions is plotted vs. the cumulative emission, i.e., the fractional contribution of all leaks of a given size or larger. Four distributions of emissions are plotted from published studies representing Barnett emissions in 2013 (red trace) (Fig. 2(c) in [41]), a compilation of published emissions between 2011 and 2016 [component-level: yellow trace (Fig. 5 in [42]); all sources: purple trace (Worksheet S1 in [42])], and Permian emissions in late 2019 (blue trace) (Fig. 2(b) in [15]). Also plotted is a scaled distribution of the Permian emissions (green dashed trace) to approximately correct for the higher detection limit of the Cusworth et al. [59] method, which may not fully account for medium-sized leaks. For comparison, approximate detection limits for satellite-, aircraft-, and ground-based emission quantification are shown. Where the detection limit lines cross the emission distribution traces indicates the fraction each method can detect of the total emission. We note that some of these studies occurred several years ago and may not reflect emissions under current regulatory or infrastructure regimes. *The aircraft detection limit is for LIDAR at wind speeds $<2$ m/s. The detection limit increases with wind speed [43]. Detection limits are higher for mass balance (3–5 kg/hr) and airborne imaging spectrometers (10–30 kg/hr). The satellite detection limit of 500 kg/hr is that stated by Irakulis-Loitxate et al. [44], although the detection limit of 100 kg/hr, stated by Jervis et al. [45] for the latest GHGSat detection limits, is shown for comparison. As of the writing of this report, the lower detection limit has not been verified in the peer-reviewed literature.

Figure 4

Component emissions and measurement detection threshold. Single-source methane emissions are plotted for various components of natural gas production in the Barnett Shale region of Texas [41]. The average emissions are shown with red bars; the maximum expected emissions are shown with blue bars. Overlaid are the detection limits for emissions using ground-, airborne-, and satellite-based technologies. Note the breaks in the scale of the $y$-axis. Detection limits are determined from peer-reviewed literature for ground-based [51], airborne [43, 52, 53] and spaceborne [45] emission detection. *Note that the spaceborne detection limit shown here is based on predicted capabilities of next generation GHGSat systems. The current detection limit demonstrated in practice is 500 kg/hr [44].

Figure 5

Example of the standoff ground-based emissions monitoring approach (image provided by LongPath Technologies). A single laser spectrometer sequentially measures along several kilometer-scale beam paths to look for leaks in an oil and gas region. Cost reduction is achieved by the fact that a single system can sensitively monitor many assets in a 1- to 2-mile radius [51].

Figure 6

Example leak detected from an airborne gas mapping LIDAR system provided by Bridger Photonics. High spatial resolution and overlaid aerial photography greatly simplify the process of identifying the leak source [43].