Facility level measurement of offshore oil and gas installations from a medium-sized airborne platform: method development for quantification and source identification of methane emissions
Résumé
Emissions of methane (CH4)from offshore oil andgas installations are poorly ground-truthed, and quantifica-tion relies heavily on the use of emission factors and activ-ity data. As part of the United Nations Climate & Clean AirCoalition (UN CCAC) objective to study and reduce short-lived climate pollutants (SLCPs), a Twin Otter aircraft wasused to survey CH4emissions from UK and Dutch offshoreoil and gas installations. The aims of the surveys were to(i) identify installations that are significant CH4emitters,(ii) separate installation emissions from other emissions us-ing carbon-isotopic fingerprinting and other chemical prox-ies, (iii) estimate CH4emission rates, and (iv) improve fluxestimation (and sampling) methodologies for rapid quantifi-cation of major gas leaks.In this paper, we detail the instrument and aircraft set-up for two campaigns flown in the springs of 2018 and2019 over the southern North Sea and describe the devel-opments made in both the planning and sampling methodol-ogy to maximise the quality and value of the data collected.We present example data collected from both campaigns todemonstrate the challenges encountered during offshore sur-veys, focussing on the complex meteorology of the marineboundary layer and sampling discrete plumes from an air-borne platform. The uncertainties of CH4flux calculationsfrom measurements under varying boundary layer conditionsare considered, as well as recommendations for attributionof sources through either spot sampling for volatile organiccompounds (VOCs)/δ13CCH4or using in situ instrumentaldata to determine C2H6–CH4ratios. A series of recommen-dations for both planning and measurement techniques forfuture offshore work within marine boundary layers is pro-vided
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