Methane emissions from oil and gas platforms in the North Sea.

Since 1850 the concentration of atmospheric methane (CH4), a potent
greenhouse gas, has more than doubled. Recent studies suggest that
emission inventories may be missing sources and underestimating emissions.
To investigate whether offshore oil and gas platforms leak CH4 during
normal operation, we measured CH4 mole fractions around eight oil and gas
production platforms in the North Sea which were neither flaring gas nor
off-loading oil. We use the measurements from summer 2017, along with
meteorological data, in a Gaussian plume model to estimate CH4 emissions
from each platform. We find CH4 mole fractions of between 11 and 370 ppb
above background concentrations downwind of the platforms measured,
corresponding to a median CH4 emission of 6.8 g CH4 s-1 for each platform,
with a range of 2.9 to 22.3 g CH4 s-1. When matched to production records,
during our measurements individual platforms lost between 0.04% and 1.4%
of gas produced with a median loss of 0.23%. When the measured platforms
are considered collectively, (i.e. the sum of platforms’ emission fluxes
weighted by the sum of the platforms’ production), we estimate the CH4
loss to be 0.19% of gas production. These estimates are substantially
higher than the emissions most recently reported to the National
Atmospheric Emission Inventory (NAEI) for total CH4 loss from United
Kingdom platforms in the North Sea. The NAEI reports CH4 losses from the
offshore oil and gas platforms we measured to be 0.13% of gas production,
with most of their emissions coming from gas flaring and offshore oil
loading, neither of which were taking place at the time of our
measurements. All oil and gas platforms we observed were found to leak CH4
during normal operation and much of this leakage has not been included in
UK emission inventories. Further research is required to accurately
determine total CH4 leakage from all offshore oil and gas operations and
to properly include the leakage in national and international emission
inventories.

自1850年以来，大气甲烷（CH₄）——一种强效温室气体——的浓度已增加一倍以上。近期研究表明，排放清单可能遗漏了部分排放源，且低估了排放量。为探究海上油气平台在正常运行期间是否泄漏CH₄，我们对北海8座既不进行火炬燃烧也不卸载石油的油气生产平台周边的CH₄摩尔分数进行了测量。我们利用2017年夏季的测量数据及气象数据，通过高斯羽流模型估算各平台的CH₄排放量。结果显示，在被测平台下风处，CH₄摩尔分数较背景浓度高出11至370 ppb，对应各平台CH₄排放中位数为6.8 g CH₄ s⁻¹，范围为2.9至22.3 g CH₄ s⁻¹。与生产记录匹配后发现，测量期间单个平台的气体损失率介于0.04%至1.4%之间，中位数为0.23%。综合考虑所有被测平台时（即平台排放通量总和按平台产量总和加权），我们估算CH₄损失率为气体产量的0.19%。这些估算值显著高于英国北海平台向国家大气排放清单（NAEI）最新报告的总CH₄损失量。NAEI报告显示，我们所测海上油气平台的CH₄损失率为气体产量的0.13%，且其大部分排放来自火炬燃烧和海上石油卸载——而这两种活动在我们测量期间均未发生。我们观察到的所有油气平台在正常运行期间均存在CH₄泄漏，且大部分此类泄漏未被纳入英国排放清单。需进一步研究以准确确定所有海上油气作业的CH₄总泄漏量，并将其妥善纳入国家及国际排放清单中。