Airborne quantification of Angolan offshore oil and gas methane emissions

Abstract. In September 2022, the METHANE-To-Go Africa (MTGA) scientific aircraft campaign, part of UNEP’s IMEO Methane Science Studies, conducted the first CH₄ emissions measurements from the offshore oil and gas sector in West Africa. This study provides the first independent empirical data on emissions in this previously unstudied region. Emissions from Angolan offshore facilities were quantified using an aircraft-based mass balance method, estimating total sector emissions and assessing 30 individual facilities and 10 facility groups.

Our findings show consistent emissions across different days for most facilities. However, high-emission events of 10 and 4 t h⁻¹ were observed at two facilities, significantly impacting total emissions. Older, low-producing shallow-water facilities had higher emissions than newer, high-producing deep-water facilities. Production volume is a poor proxy for methane emissions; instead, facility age and maintenance status should be considered risk factors. However, due to variations in asset design and operation, regular measurements are essential, prioritizing high-risk facilities.

Total CH₄ emissions from Angolan offshore facilities were estimated at 16.9 ± 5.3 t h⁻¹, only 20–22 % of EDGAR and CAMS estimates but over twice the amount reported by operators. Additional trace gas measurements, including CO₂, CO, C₂H₆, SO₂, NOy, and aerosols, provided insights into CH₄ sources, primarily from fugitive emissions and venting rather than flaring or combustion. This study presents a unique dataset on CH₄ emissions, improving our understanding of offshore oil and gas emissions in this critical region.