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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 offloading 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 was 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. [ABSTRACT FROM AUTHOR]

Recent studies suggest oil and natural gas production facilities in North America may be underestimating methane (CH4) emissions during extraction. This, coupled with unusually high CH4 mole fractions observed at coastal sites during onshore winds in the UK, suggests CH4 emissions from oil and gas extraction activities in the North Sea could be higher than previously reported. To investigate if these coastal CH4 enhancements could have come from oil and gas production platforms, we use near-source measurement techniques to estimate CH4 emissions from eight oil and gas production platforms in the North Sea. We estimate the mean CH4 emission from the eight platforms to be 10.1 g CH4 s−1, with a range of 1.1 to 25.0 g CH4 s−1. When matched to production records, individual platforms lose between 0.01 % and 1.58 % of gas production with an average loss of 0.61 % of gas production. However, when the measured platforms are considered collectively, i.e. when the total measured emission is compared to total production of the platforms measured, the CH4 loss is estimated at 0.27 % of gas production. These calculated ranges are at least double the most recently reported loss rates for these platforms, which are currently estimated at 0.13 % of gas production. In fact, the vast majority of reported emissions are due to gas flaring and offshore oil loading, neither of which was taking place at the time of these measurements. If emissions measured here resulted from leakage during normal operation, they represent significant additional emissions (at least 0.27 % of production) above previous estimates of CH4 leakage from off-shore oil and gas production platforms. These emissions are not explicitly included in UK emission inventories. Further research to determine CH4 leakage from all operations occurring at off-shore oil and gas platforms, and how to include them in national emission inventories, is needed. [ABSTRACT FROM AUTHOR]