Use of Light Alkane Fingerprints in Attributing Emissions from Oil and Gas Production

Abstract

Spatially resolved emission inventories were used with an atmospheric dispersion model to predict ambient concentrations of methane, ethane, and propane in the Eagle Ford oil and gas production region in south central Texas; predicted concentrations were compared to ground level observations. Using a base case inventory, predicted median propane/ethane concentration ratios were 106% higher (95% CI: 83% higher–226% higher) than observations, while median ethane/methane concentration ratios were 112% higher (95% CI: 17% higher–228% higher) than observations. Predicted median propane and ethane concentrations were factors of 6.9 (95% CI: 3–15.2) and 3.4 (95% CI: 1.4–9) larger than observations, respectively. Predicted median methane concentrations were 7% higher (95% CI: 39% lower–37% higher) than observations. These comparisons indicate that sources of emissions with high propane/ethane ratios (condensate tank flashing) were likely overestimated in the inventories. Because sources of propane and ethane emissions are also sources of methane emissions, the results also suggest that sources of emissions with low ethane/methane ratios (midstream sources) were underestimated. This analysis demonstrates the value of using multiple light alkanes in attributing sources of methane emissions and evaluating the performance of methane emission inventories for oil and natural gas production regions.

Forward Modeling and Optimization of Methane Emissions in the South Central United States Using Aircraft Transects Across Frontal Boundaries

“…From this experiment, we find that applying a flat C 2 H 6 :CH 4 ratio of 0.13 produces solutions for O&G emissions using the C 2 H 6 optimization that are nearly identical to the solutions from the CH 4 optimization both overall and flight-by-flight, with an absolute mean difference between the O&G rates per flight from these two solutions of only 0.15. The strong correlation between the results of these two optimizations after increasing the C 2 H 6 :CH 4 ratio by 80% of its original value (0.13 vs 0.07) indicates that C 2 H 6 :CH 4 emission ratios used in the simplified C 2 H 6 inventory may be significantly lower than the true ratios, and could be related to an underestimation of emissions from oil-producing sectors of basins with a much lower percentage of CH 4 content (Gherabati et al, 2016;Cardoso-Saldaña et al, 2019).…”

Aggregation and Allocation of Greenhouse Gas Emissions in Oil and Gas Production: Implications for Life-Cycle Greenhouse Gas Burdens

“…Wells are grouped into 12 distinct production regions, based on the American Petroleum Institute (API) gravity of the liquids produced, and the GOR of the wells (see Supporting Information). , Based on production characteristics, well site conditions and well stream compositions, Cardoso-Saldaña et al developed a thermodynamic model to determine the compositions of individual molecular species in produced gas streams and condensate streams of each region (see Supporting Information). These molecular compositions of produced gas and condensate flows are assigned to individual wells based on the well locations.…”

“…Methane emissions (fugitive and nonfugitive) from well site operations by source category in the Eagle Ford Shale are derived from the emission inventory developed by Cardoso-Saldaña et al, for the 2013 calendar year . A base year of 2013 was chosen by Cardoso-Saldaña et al to enable comparisons with other production regions and comparisons with ambient observations of light hydrocarbon concentrations.…”

“…Calendar year 2013 data are used in the analyses since emission estimates, evaluated against ambient observations, have been published for this period. Cardoso-Saldaña, et al, report that emissions of methane in the Eagle Ford Shale production region are dominated by flashing from condensate tanks. Therefore, methane emissions are more extensive in the oil-rich portions of the region and are largely due to the parts of the supply chain (e.g., condensate tanks) associated with liquids (oil and condensate production).…”

Facility level measurement of offshore oil and gas installations from a medium-sized airborne platform: method development for quantification and source identification of methane emissions

“…Some of these VOCs are toxic and can have direct health impacts or, together with NO x , can produce ozone, having an impact on the regional air quality (Edwards et al, 2013). VOC and δ 13 C CH4 measurements can be utilised to fingerprint the main processes or likely location responsible for associated CH 4 emissions (Cardoso-Saldaña et al, 2019;Lee et al, 2018;Yacovitch et al, 2014a).…”