Temporal Variation and Persistence of Methane Emissions from Shallow Water Oil and Gas Production in the Gulf of Mexico

Methane emissions from the oil and gas supply chain can
be intermittent,
posing challenges for monitoring and mitigation efforts. This study
examines shallow water facilities in the US Gulf of Mexico with repeat
atmospheric observations to evaluate temporal variation in site-specific
methane emissions. We combine new and previous observations to develop
a longitudinal study, spanning from days to months to almost five
years, evaluating the emissions behavior of sites over time. We also
define and determine the chance of subsequent detection (CSD): the
likelihood that an emitting site will be observed emitting again.
The average emitting central hub in the Gulf has a 74% CSD at any
time interval. Eight facilities contribute 50% of total emissions
and are over 80% persistent with a 96% CSD above 100 kg/h and 46%
persistent with a 42% CSD above 1000 kg/h, indicating that large emissions
are persistent at certain sites. Forward-looking infrared (FLIR) footage
shows many of these sites exhibiting cold venting. This suggests that
for offshore, a low sampling frequency over large spatial coverage
can capture typical site emissions behavior and identify targets for
mitigation. We further demonstrate the preliminary use of space-based
observations to monitor offshore emissions over time.