Modeling near-field dispersion from direct injection of carbon dioxide into the ocean

In this paper we have predicted the dynamics of double plume formation and dispersion from direct injection of liquid CO2 into middle-depth ocean water. To do so, we used a three-dimensional, two-fluid numerical model. The model consists of a CO2 droplet submodel and a small-scale turbulent ocean submodel, both of which were calibrated against field observation data. With an injection rate of 100 kg s-1 CO2, numerical simulations indicated that the injection of 8-mm-diameter CO2 droplets from fixed ports at 858 m (20 m above the seafloor) into a current flowing at 2.5 cm s-1 could create a plume that reaches the bottom and has at most a 2.6-unit decrease in pH. The strong interaction between the buoyant rise of the liquid CO2 and the fall of the CO2-enriched water produced a vertically wavy plume tip at about 190 m above the seafloor. The maximum pH decrease, however, was kept to 1.7 units when the liquid CO2 had an initial droplet diameter of 20 mm and it was injected at 1500 m from a towed pipe with a ship speed of 3.0 m s-1. After 70 min the double plume developed into a single-phase passive plume with a vertical scale of 450 m and a horizontal scale larger than 150 m. This development was attributable to the droplets' buoyant rise and dissolution, along with ocean turbulence, which together diluted the plume and reduced the decrease in pH to less than 0.5 units.