Abstract
The oil and gas (O&G) sector is a significant source of methane (CH4) emissions. Quantifying these emissions remains challenging, with many studies highlighting discrepancies between measurements and inventory-based estimates. In this study, we present CH4 emission fluxes from 21 offshore O&G facilities collected in 10 O&G fields over two regions of the Norwegian continental shelf in 2019. Emissions of CH4 derived from measurements during 13 aircraft surveys were found to range from 2.6 to 1200g tyr-1 (with a mean of 211g tyr-1 across all 21 facilities). Comparing this with aggregated operator-reported facility emissions for 2019, we found excellent agreement (within 1? uncertainty), with mean aircraft-measured fluxes only 16g % lower than those reported by operators. We also compared aircraft-derived fluxes with facility fluxes extracted from a global gridded fossil fuel CH4 emission inventory compiled for 2016. We found that the measured emissions were 42g % larger than the inventory for the area covered by this study, for the 21 facilities surveyed (in aggregate). We interpret this large discrepancy not to reflect a systematic error in the operator-reported emissions, which agree with measurements, but rather the representativity of the global inventory due to the methodology used to construct it and the fact that the inventory was compiled for 2016 (and thus not representative of emissions in 2019). This highlights the need for timely and up-To-date inventories for use in research and policy. The variable nature of CH4 emissions from individual facilities requires knowledge of facility operational status during measurements for data to be useful in prioritising targeted emission mitigation solutions. Future surveys of individual facilities would benefit from knowledge of facility operational status over time. Field-specific aggregated emissions (and uncertainty statistics), as presented here for the Norwegian Sea, can be meaningfully estimated from intensive aircraft surveys. However, field-specific estimates cannot be reliably extrapolated to other production fields without their own tailored surveys, which would need to capture a range of facility designs, oil and gas production volumes, and facility ages. For year-on-year comparison to annually updated inventories and regulatory emission reporting, analogous annual surveys would be needed for meaningful top-down validation. In summary, this study demonstrates the importance and accuracy of detailed, facility-level emission accounting and reporting by operators and the use of airborne measurement approaches to validate bottom-up accounting.
| Original language | English |
|---|---|
| Pages (from-to) | 4303-4322 |
| Number of pages | 20 |
| Journal | Atmospheric Chemistry and Physics |
| Volume | 22 |
| Issue number | 7 |
| DOIs | |
| Publication status | Published - 4 Apr 2022 |
Bibliographical note
© Author(s) 2022.Funding Information:
Acknowledgements. This work was supported by the Climate and Clean Air Coalition (CCAC) Oil and Gas Methane Science Studies (MSS) hosted by the United Nations Environment Programme. Funding was provided by the Environmental Defense Fund, the Oil and Gas Climate Initiative, the European Commission, and CCAC (reference no. DTIE19-020). The data used in this publication were collected as part of the Methane Observations and Yearly Assessments (MOYA) project funded by the Natural Environment Research Council (NERC) (The Global Methane Budget, University of Manchester, reference no. NE/N015835/1; Royal Hol-loway, University of London, reference no. NE/N016211/1). Air-borne data were obtained using the BAe-146 atmospheric research aircraft and the Mooney Acclaim aircraft. The former was flown by Airtask Ltd and managed by FAAM Airborne Laboratory, jointly operated by UK Research and Innovation (UKRI) and the University of Leeds. The latter was flown and managed by Scientific Aviation. We would like to give special thanks to the Airtask pilots and engineers and all staff at the FAAM Airborne Laboratory, as well as the pilots from Scientific Aviation for their hard work in helping plan and execute successful MOYA project flights. We would also like to thank staff at Kiruna Airport, Norway, for hosting the FAAM aircraft during the campaign.
Funding Information:
The FAAM research aircraft conducted three regional flight surveys of two regions on the Norwegian continental shelf in July and August 2019, as part of the “Methane Observations and Yearly Assessments” (MOYA) project, funded jointly by the Natural Environment Research Council (NERC) and the United Nations Environment Programme Climate and Clean Air Coalition (UNEP CCAC). Figure 1 illustrates the two regions surveyed by the flights, along with O&G facilities in the area.
Funding Information:
Correspondence: Grant Allen ([email protected])
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