Journal
ENVIRONMENTAL SCIENCE & TECHNOLOGY
Volume 54, Issue 6, Pages 3530-3538Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.est.9b07148
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Funding
- Climate and Clean Air Coalition (CCAC) Oil and Gas Methane Science Studies
- Environmental Defense Fund
- OGCI Company (Shell)
- OGCI Company (BP)
- OGCI Company (ENI)
- OGCI Company (Petrobras)
- OGCI Company (Repsol)
- OGCI Company (Total)
- OGCI Company (Equinor)
- OGCI Company (CNPC)
- OGCI Company (Saudi Aramco)
- OGCI Company (Pemex)
- CCAC
- European Commission
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Shipboard measurements of offshore oil and gas facilities were conducted in the Gulf of Mexico in February 2018. Species measured at 1 s include methane, ethane, carbon-13 (C-13) and deuterium (D) isotopes of methane, and several combustion tracers. Significant variability in the emission composition is observed between individual sites, with typical ethane/methane ratios around 5.3% and C-13 and D methane isotopic compositions around -40 and -240%c, respectively. Offshore plumes were spatially narrower than expectations of the plume width based on terrestrial atmospheric stability classes; a modified Gaussian dispersion methodology using empirically measured horizontal plume widths was used to estimate the emission rates. A total of 103 sites were studied, including shallow and deepwater offshore platforms and drillships. Methane emission rates range from 0 to 190 kg/h with 95% confidence limits estimated at a factor of 10. The observed distribution is skewed with the top two emitters accounting for 20% of the total methane emissions of all sampled sites. Despite the greater throughput of the deepwater facilities, they had moderate emission rates compared to shallow-water sites. Analysis of background ethane enhancements also suggests a source region in shallow waters. A complete 1 s measurement database is published for use in future studies of offshore dispersion.
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