Tuesday, December 17, 2013

Hi! I'm CJ Beegle-Krause, a researcher at SINTEF, in Trondheim, Norway. I work with a large group of people working to better understand oil spills. Some people work on the chemistry and toxicity of oil, while my team works on computer modeling of the oil in order to answer many questions such as "Where does the oil go?", "How does the oil change in the environment?", and "What are the potential environmental impacts of the oil?" Additionally, we have some people working on how to clean up spilled oil. We  perform laboratory and open ocean field work with oil as well as develop computer models.

The picture above shows two types of spills: a leaking ship and a subsurface well. The oil will be located on the water surface and in the water column. Collecting oil with a towed boom and application of chemical dispersants from a helicopter are two response options shown in the picture, though there are more options such as in situ burning. Models can help responders evaluate different response measures as they formulate their plans. Winds and waves can disperse oil into the water column as droplets, and chemical dispersants also change the surface oil into smaller droplets in the water column.  In the DROPPS project we are working to improve modeling of the droplet related processes, particularly related to potentially applying chemical dispersants. A great deal of research goes into making a computer model appropriate for making decisions in real life situations.

For oil droplets, how small is small? Let's talk in terms of a human hair, which ranges in diameter from 17µm (pale blonde) to 181µm (black) (Thanks Wikipedia![1]). The lower end of this range is at the limit of what the human eye can perceive.

Oil droplets are small, but they are big news in understanding the movement and potential impacts of oil spills. The rise speed of an oil droplet is proportional to the droplet's diameter. Droplets that you can barely see will rise very slowly. Larger droplets, say millimeters in diameter, will rise more quickly, and can reach the ocean surface in a matter of hours from deep in the ocean. Smaller droplets take longer to rise, and very small droplets at ~10 µm in diameter are too small to rise, as they are trapped by friction with the water.
The mini Tower Basin

Why is something so small so important? The droplet size distribution determines how much of the oil will remain within the ocean, and how much will rise at the surface. During an oil spill, responders may have the option to add chemical dispersants to the spill, either from the surface or subsurface, to alter the droplet. Chemical dispersants break up oil into smaller droplets, so more of the oil stays within the water column. If a spill is in an area with many water birds, keeping as much oil as possible in the water column may be better, so chemical dispersants might be used immediately. On the other hand, if the spill is in a sensitive coral reef area, leaving the oil at the surface may be better, with cleanup using booms and skimmers to remove surface oil. In the US, response decisions are made jointly within the Unified Command, whose members include the U.S. Coast Guard, Trustee Federal and State Agencies, and the responsible party. They use output from computer models to evaluate the oil spill’s predicted path and any changes in the oil location from the potential use of chemical dispersants.

The Tower Basin

SINTEF has a new Tower Basin, which is 6 m high and 2 m wide: a big tank for making small droplets. We use it to simulate deepwater well blowouts. We do experiments to release different oil types under pressure through a small nozzle, and use different chemical dispersant ratios injected into the rising plume of oil droplets to change the droplet size distribution.

The modeling group works to put together the laboratory and field work with mathematical models in order to make predictions about where the oil will go in an oil spill, and how one might clean that oil up. We work on software called OSCAR (Oil Spill Contingency And Response) and DREAM (Does-related Risk and Effect Assessment Model). These models help people plan for and respond to oil spills.

Members of the Sintef modeling group