Characterizing Equipment-Specific Ethane–Methane Ratios to Inform Top-Down

Winrose Mollel1, Arthur Santos1, Mercy Mbua2, Jeffrey Nivitanont3, Shane Murphy3, Anna Hodshire2, Daniel Zimmerle1

1CSU Energy Institute, Colorado State University, 2 Systems Engineering Department, Colorado State University, 3Department of Atmospheric Science, University of Wyoming​

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Background​

  • Top-down(TD) methods quantify emissions but struggle to separate thermogenic (oil & gas) from biogenic sources.​
  • Ethane is co-emitted with methane in thermogenic sources, and using ethane methane ratios (C2/C1) helps distinguish thermogenic (oil & gas) from biogenic (wetlands, livestock, landfills) sources. ​
  • This study combines field measurements with the MAES model to determine equipment-specific C2/C1 ratios in the Denver-Julesburg Basin, improving attribution accuracy and guiding more effective emission reduction strategies.​
A drone landing at METEC
A METEC research vehicle testing at an oil and gas production site.

Methodology​

  • MAES-simulated molar C2/C1 ratios were generated using data from CDPHE’s ONGAEIR 2022 emissions inventory in combination with SABER aerial flight data, incorporating failures and missing sources, operator-reported equipment activity, and facility equipment configurations. ​
  • Field measurements were collected from 163 production and midstream facilities in the DJ basin by Colorado State University and the University of Wyoming during two phases of the 2024 SABER flight campaign: one in the summer (Summer Drive) and another in the fall (Fall Drive). ​
  • The analysis focuses on wells, separators, compressors, tanks, and flares.
Emissions do not correspond with the site shown. Visuals created for marketing and training purposes only. © Bridger Photonics.

Results​

  • As seen in Figure 1, flares and tanks exhibit the highest ratios, separators show moderate values, compressors remain consistently low, and wellheads display the lowest ratios across all datasets.​
Molar Ethane Methane Ratio on the y-axis. X-axis data is first grouped by MAES, Summer Drive, and Fall Drive. These are broken down into equipment types, including Compressor, Flare, Separator, Tank, and Wellhead.
Figure 1: Molar C2/C1 ratios by equipment type from MAES simulations, the 2024 Summer Drive campaign, and the 2024 Fall Drive campaign. Across all datasets, tanks and flares exhibited the highest C2/C1 ratios, while compressors, separators, and wellheads showed consistently lower values.​
  • Simulated values often fall within the observed ranges but tend to either
    overestimate or underestimate absolute ratios due to differences in operational
    conditions, gas composition, and modeling assumptions. ​​
  • As shown in Figure 2, failure conditions can substantially alter the C2/C1 ratio, particularly in flares and tanks. Monitoring the C2/C1 ratio could therefore serve as a practical screening tool for detecting abnormal emissions at the equipment
    level.
Figure 2: Routine vs. failure molar C2/C1 ratio across MAES simulation results and summer and fall ground measurements. Two boxplots are shown per equipment group: one representing the C2/C1 ratio range for normal operations and the other for failure conditions.​

Conclusions and Next Steps

  • Equipment-specific C2/C1 ratio variation: Ethane–methane ratios differ widely across sources and operating conditions; using a single wellhead value biases TD emission attribution. Relative to the basin ratio (0.101), tanks (9×), flares (12.5×), separators (~2.7×), compressors (1.4×), and wellheads (1.66×) show substantial enrichment, meaning a single ratio underestimates ethane-rich
    sources while overestimating methane-rich ones.​
  • Equipment-level ratios enhance model–field alignment, diagnostics, and inventories, especially for ethane-rich sources (tanks, flares).​
  • Path forward for improved attribution: Integrating mechanistic MAES modeling with high-resolution ground measurements (e.g., SABER) enables source- and event-specific emission characterization.
Measurement-Informed Inventory: State Inventory and Aerial Surveys to MAES (Mechanistic Air Emissions Simulator) to Corrected DJ Basin CH4 Inventory +16.4%

Acknowledgments and Contact Information

This material is based upon work supported by the Department of Energy under award DEFE0032288.

We thank Bridger Photonics, the Center for Air Quality (CAQ) at the University of Wyoming, and the Earth-Atmosphere Interactions Lab at The Pennsylvania State University for their contributions.

Winrose Mollel 
CSU Energy Institute, Colorado State University
[email protected]


References​

  1. H. M. Daley, R. R. R. Dickerson, P. R. Stratton, H. He, X. Ren, A. Koss, A. Brewer, S. Baidar, B. Hmiel, D. Bon, G. Pierce, P. Weibring, D. Richter, J. Walega, M. Ngulat, A. Santos, A. L. Hodshire, T. Vaughn, D. Zimmerle, A. Fried, Methane and Ethane Emission Rates, Intensities, and Trends: Aircraft Mass Balance Insights over the Denver-Julesburg Basin, Fall 2021.​
  2. Z. R. Barkley, K. J. Davis, S. Feng, Y. Y. Cui, A. Fried, P. Weibring, D. Richter, J. G. Walega, S. M. Miller, M. Eckl, A. Roiger, A. Fiehn, J. Kostinek, Analysis of Oil and Gas Ethane and Methane Emissions in the Southcentral and Eastern United States Using Four Seasons of Continuous Aircraft Ethane Measurements, Journal of Geophysical Research: Atmospheres 126 (10) (2021) e2020JD034194. doi:10.1029/2020JD034194.​
Equipment at the METEC Site