Abstract
Abstract. 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.
Highlights
Methane (CH4) is a greenhouse as well as a precursor of tropospheric ozone, which is widely regulated as a component of photochemical smog
Several activities on offshore production platforms in the North Sea are explicitly identified by the BEIS in the National Atmospheric Emission Inventory (NAEI) as sources of CH4 emission including combustion activities such as gas flaring, offshore oil loading and venting directly to the atmosphere (BEIS, 2018)
In this study we investigate CH4 emissions from offshore oil and gas installations in the North Sea and determine how they differ from those currently reported by the BEIS
Summary
Methane (CH4) is a greenhouse as well as a precursor of tropospheric ozone, which is widely regulated as a component of photochemical smog. Riddick et al.: Methane emissions from oil and gas platforms in the North Sea. Observatory (WAO; 52.95◦ N, 1.14◦ E) during periods of northerly onshore winds and high surface pressures (Connors, 2015; Staunton-Sykes, 2016; Connors et al, 2018). Recent studies indicate public inventories in the United States underestimate CH4 emissions, including from the oil and gas supply chain (Alvarez et al, 2018; Zavala-Araiza et al, 2015; Schwietzke et al, 2017). Several activities on offshore production platforms in the North Sea are explicitly identified by the BEIS in the National Atmospheric Emission Inventory (NAEI) as sources of CH4 emission including combustion activities such as gas flaring, offshore oil loading and venting directly to the atmosphere (BEIS, 2018). The CH4 loss is presented as a percentage of the CH4 produced by each platform
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