Brandvik, P. J. (SINTEF) | Johansen, Ø. (SINTEF) | Davies, E. J. (SINTEF) | Leirvik, F. (SINTEF) | Krause, D. F. (SINTEF) | Daling, P. S. (SINTEF) | Dunnebier, D. (SINTEF) | Masutani, S. (University of Hawaii) | Nagamine I, I. (University of Hawaii) | Storey, C. (Swri) | Brady, C. (Swri) | Bellore, R. (SL Ross Environmental Research) | Nedwed, T. (ExxonMobil Upstream Research Company) | Cooper, C. (Chevron Energy Technology Corporation) | Ahnell, A. (BP Upstream HSE) | Pelz, O. (BP Upstream HSE) | Anderson, K. (Shell Projects & Technology)
This paper presents novel results regarding the effectiveness of subsea dispersant injection relevant for operational guidance, decision making and to improve existing models describing the environmental fate and behavior of subsea releases of oil and gas. More specifically, the paper presents data from a comprehensive set of laboratory experiments to evaluate the formation, fate, and transition of dispersed oil droplets in the water column during a subsea oil and gas blowout in combination with subsea dispersant injection (SSDI).
Many sub-sea well blowout oil and gas release scenarios form relatively large oil droplets (multiple millimeters), which then rapidly rise through the water column to form thick slicks on the ocean surface, potentially very near the source. On the other hand, smaller oil droplets (< 500 microns) rise more slowly and can stay suspended in the water column for days to weeks. Dispersant injection is therefore warranted to reduce the potential for floating oil and associated volatile hydrocarbons that may threaten worker health and safety, and reach ecologically and economically sensitive surface water and shoreline environments. The oil that disperses into the water column may pose temporary elevated exposures to organisms in the immediate area, but research and experience has shown that those exposures are rapidly mitigated by the effects of dilution and microbial degradation of the dispersed oil.
The results of our laboratory studies, which examined the influence of different variables on the initial oil droplet size in an oil release scenario (including oil release velocity, dispersant dosage, dispersant injection method, oil temperature, high pressure, gas-to-oil ratio, oil- and dispersant characteristics), revealed that dispersant injection is highly effective at reducing droplet size. Our data also fit a new modified Weber Number scaling algorithm that can be used to calculate initial oil droplet size at field scales. Model simulations using the new modified Weber number scaling indicate that SSDI can reduce droplet size by an order of magnitude which serves to delay and significantly reduce surfacing of oil from large oil spills.
In summary, this paper describes the results of a substantial research program that studied the effectiveness of SSDI. This research shows that SSDI applied directly to oil flowing from a well blowout is a highly efficient oil spill response tool to substantially reduce the surfacing of oil by reducing oil droplet size thereby enhancing worker safety and providing a net environmental benefit.