Methane Emissions from Offshore Oil and Gas Platforms in the Gulf of Mexico

C and D methane isotopic compositions around -40 and -240‰, 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.