Simulation of oil-gas releases including dispersant application with special focus on droplet size distributions - Experimental concept and some initial results

Simulation of DWH Oil/Gas Releases Including Dispersant Application, with Focus on Droplet Size Distributions Experimental Concept and Initial Results P.J. Brandvik, O. Johansen, F. Leirvik, P. Daling, SINTEF, Materials and Chemistry, Marine Environmental technology. During the initial phase of the Deep Water Horizon (DWH) incident oil and gas were released from two locations on the broken riser and one on the drill pipe. Later the riser was removed and oil and gas were released from a single location on top of the BOP. Subsea dispersant was injected into the released oil and gas stream at varying locations. The size and distribution of oil droplets is believed to affect such factors as the time required for oil to rise to the surface, the location where it surfaces, dissolution in the water column, and entrainment of the smallest droplets beneath deepwater density layers. There were no immediate deepwater in-situ measurements of oil droplet sizes at the various release points, or at the location of subsea dispersant injection into the turbulent deep water release. The first focus area of this project is to simulate the release of oil and gas from a hypothetical subsea blowout in order to increase our knowledge regarding the droplet size and distribution of released oil. The second focus area is to study different application techniques for deep water dispersant application and their influence on droplet size and distribution. A Tower tank is established at SINTEF for this purpose. The tank is 6 meters high, 3 meters wide and holds 40m3 of natural sea water. The tank is equipped with an advanced system for releasing oil and gas, and monitoring oil droplet size distributions and oil concentrations in the released plume. The droplet size distributions are measured with three independant in-situ methods (laser particle sizer, particle visual microscope and a macro camera with a blue-laser focusing plane). Different methods are studied to inject dispersants into the hydrocarbon stream. Although the tower cannot reproduce the temperature and pressure conditions encountered in a deep water release, the experimental conditions will exceed bench scale tests by at least one order of magnitude. We will review the assumptions needed to mathematically scale these results to the conditions involved in a deepwater release. Our aim is to use the broad range of experimental conditions possible with this basin to provide more confident extrapolations to full scale conditions. The experimental concept of the tower basin and initial results with oil alone, oil/gas and with dispersant will be presented.