Lawrence Berkeley National Laboratory

Growing interest in offshore geologic carbon sequestration (GCS) motivates risk assessment of large-scale subsea CO2 well blowouts or pipeline ruptures. For major leaks of CO2 from wells or pipelines, significant fluxes of CO2 may occur from the sea surface depending on water depth. In the context of risk assessment of human health and safety, we have used previously simulated coupled well-reservoir and water column model results as a source term for dense gas dispersion of CO2 above the sea surface. The models are linked together by one-way coupling, that is, output of one model is used as input to the next model. These first-of-their-kind coupled flow results are applicable to assessing the hazard of CO2 to people at and downwind of the sea surface location of emission. Hazard is quantified by plotting the downwind dispersion length (DDL), which we define in the study as the distances from the emission source to the point at which the emitted CO2 has been diluted to 5% and 1.5% in air by volume. Results suggest that large-scale blowouts in shallow water (10 m) may cause hazardous CO2 plumes extending on the order of several hundred meters downwind. Details of the modeling show DDL has a maximum for windspeed (at an elevation of 10 m) of approximately 5 m/s, with smaller DDL for both weaker and stronger winds. This is explained by the fact that wind favors transport but also causes dispersion; therefore there is a certain wind speed that maximizes DDL. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd.