Quantification and assessment of methane emissions from offshore oil and gas facilities on the Norwegian Continental Shelf

Abstract

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 1200 t year−1 (with a mean of 211 t year−1 across all 21 facilities). Comparing this with aggregated operator-reported facility emissions for 2019, we found excellent agreement (within 1σ uncertainty), with mean aircraft-measured fluxes 16 % 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 42 % 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 representivity 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 prioritizing targeted emission mitigation solutions. Surveys of individual facilities may always require this. However, for field-aggregated emissions, our results show that an accurate estimate of total field-level emissions simply requires a sufficiently large and representative sample of facilities, to yield meaningful comparisons and flux statistics, irrespective of operational status information. In summary, this study demonstrates the importance and accuracy of detailed, facility-level emission accounting and reporting by operators and the use of measurement approaches to validate bottom-up accounting.

Flaring efficiencies and NOx emission ratios measured for offshore oil and gas facilities in the North Sea

“…measured much larger median CH 4 emissions of 120 g CH 4 s −1 (range: 20-360 g CH 4 s −1 ) from four facilities in the North Sea. Riddick et al (2019) measured CH 4 emissions using a shipborne platform, reporting median emissions of 6.8 g CH 4 s −1 (214 t CH 4 yr −1 ) across eight facilities, in exceptional agreement with Foulds et al (2022). In the southern North Sea, Pühl et al (2023) measured median emissions of 10 g CH 4 s −1 from a sample of UK and Dutch oil and gas platforms.…”

“…Dry mole fractions of CO 2 and CH 4 were measured using a cavity-enhanced absorption spectrometer (Fast Greenhouse Gas Analyzer (FGGA); Los Gatos Research Inc., USA), sampling air through a window-mounted rear-facing chemistry inlet. A full description of the FGGA for measurements on board the FAAM aircraft was reported by O'Shea et al (2013), with a modified instrumental setup (used after January 2019) described by Shaw et al (2022). Raw CO 2 and CH 4 mole fraction data were corrected for small effects associated with water vapour dilution and spectroscopic error.…”

“…Offshore oil and gas facilities in the North and Norwegian seas have been the subject of several studies complementary to the work presented here. Foulds et al (2022) measured CH 4 emission fluxes from 21 offshore facilities on the Norwegian continental shelf, finding mean emissions of 211 t CH 4 yr −1 (6.7 g CH 4 s −1 ) per facility. measured much larger median CH 4 emissions of 120 g CH 4 s −1 (range: 20-360 g CH 4 s −1 ) from four facilities in the North Sea.…”

Blue hydrogen must be done properly

“…A comparison of reported methane emissions and airborne measurements of methane over 21 offshore oil and gas installations on the NCS was conducted by independent third parties in 2019 16 . The comparison presented excellent agreement and low uncertainty, with mean aircraft‐measured fluxes 16% lower than annually reported values.…”

Comparing airborne algorithms for greenhouse gas flux measurements over the Alberta oil sands

“…While some airborne methods utilize eddy covariance measurements (Yuan et al, 2015;Wolfe et al, 2018), methods for sampling anthropogenic GHG emissions using aircraft tend to fall into two major categories: (i) mass-balance methods (O'Shea et al, 2014;Gordon et al, 2015;France et al, 2021;Foulds et al, 2022) and ii) spectral imaging methods (Duren et al, 2019;Tyner and Johnson, 2021;Krautwurst et al, 2021;Cusworth et al, 2022). These methods capture atmospheric fluxes using varying approaches that are affected by different biases and are complementary when creating emission budgets.…”