Significant Reduction in Ethane Emissions in the Denver‐Julesburg Basin From 2015 to 2021 From Oil and Natural Gas Operations

Abstract Top‐down studies of methane (CH 4 ) emissions often use the average ethane‐to‐methane (C 2 /C 1 ) ratio of wellhead gas in a basin to attribute emissions to thermogenic or biogenic sources. Biogenic CH 4 sources (ruminants, wetlands, landfills, and other methanogenic sources) do not co‐produce ethane (C 2 H 6 ); the presence of C 2 H 6 indicates a thermogenic CH 4 source. However, the C 2 /C 1 ratio often varies within and across basins, among emitting sources, and facility configurations. This study uses Fourier Transform Infrared Spectroscopy data from exhaust stack tests of both four‐stroke rich‐burn and four‐stroke lean‐burn engines, comparing the relative “destruction efficiency” between the engines and across species. Results show that engines combust heavier hydrocarbons more efficiently than CH 4 , as evidenced by consistently higher destruction efficiencies for C 2 H 6 across all engine types. The data indicate a preferential destruction of C 2 H 6 relative to CH 4 ; the exhaust gas C 2 /C 1 ratio is consistently lower than the fuel gas C 2 /C 1 ratio. Recent design modifications at O&G production facilities reduced both C 2 H 6 and CH 4 emissions, with a more pronounced reduction in C 2 H 6 emissions. In the Denver‐Julesburg basin in Colorado, natural gas production increased by 73.9% from 2015 to 2021. Despite these increases, the companion paper by Daley et al. (2025, https://doi.org/10.22541/essoar.175069495.52092664 ) shows that top‐down CH 4 and C 2 H 6 emissions from oil and natural gas facilities decreased by 25.3% and 63.6%, respectively. The combination of increased production and declining production‐sector emissions suggests that the relative contribution of midstream operations to basin‐wide emissions may have increased during this period.