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PETROMAKS2-Stort program petroleum

ENTrainment of oil In bREaking waves

Alternative title: Nedblanding av olje i brytende bølger

Awarded: NOK 12.1 mill.

In the ENTIRE project SINTEF Ocean, MET Norway, NTNU, Imperial college in the UK, and NOAA in the USA will collaborate to study the impact of winds and waves on the distribution of oil spilled on the ocean surface. Understanding the impact of wind and waves on the spreading and the trajectory is crucial in predicting the ultimate fate of the oil in the environment. In a rough sea with breaking waves, the oil is broken up into small droplets, which may significantly reduce the surface oil slick area, when compared to a slick existing under calm sea conditions. The main objective of our project is to study the mechanisms related to vertical mixing of oil into the water by breaking waves. This vertical mixing of surface oil controls the amount of oil that is available to spread on the surface and also impacts the horizontal transport. We are carrying out field and laboratory experiments to gain new knowledge and to develop and improve numerical models. Small scale laboratory experiments are underway in a wave flume at SINTEF Ocean to measure the sizes of oil droplets, turbulence, and estimate the amount of oil entrained into the water by breaking waves. Field studies are planned during Oil on Water (OPV) in Norway managed by NOFO, to collect similar data to laboratory studies. The field data are invaluable as they are rare and provide information under real environmental conditions such as intermittent breaking waves, that are very challenging to create in the lab. There was no OPV in 2023, and 2024 is currently under consideration and planning. The mechanisms that lead oil slicks to break up and mix down into the ocean are also relevant for air bubbles. Formation of air bubbles under breaking waves in the ocean is an important process which controls the exchange of gases between the ocean and the atmosphere. This is relevant for, among other things, climate models which need to know how fast the ocean will absorb CO2 from the atmosphere. Imperial College has extensive experience with the study of air bubbles under breaking waves, and in this project we wish to see how the same optical instruments can be used to study formation of both air bubbles and oil drolpets under waves, both in the lab and the field. The new knowledge will contribute to the development of the OSCAR model at SINTEF Ocean and OpenDrift model at MET to improve their performance in predicting the surface slick behavior. OSCAR and OpenDrift are used by oil and gas industry, consultants, researchers and regulatory agencies in Norway and internationally. Moreover, study findings will be communicated to stakeholders during the annual oil spill response forum, jointly organised by Norwegian government and industry.

When oil is spilled at sea, the entrainment of oil droplets by breaking waves is a process which to a large extent influences the short- and long-term transport and fate of the oil. The dynamic nature and intermittency of the sea surface makes modeling and studying the entrainment process a challenging task. The project will study the details of the entrainment process on small spatial scales and short time scales, through a novel combination of experimental work and high-resolution small-scale modelling. The goal is to understand the importance of the episodic nature of wave entrainment, and improve the predictability of entrainment rate, intrusion depth and droplet size distributions. Oil spill models need to describe the spatial and temporal distribution of droplets in the near-surface waters to correctly predict the transport and separation of oil into different environmental compartments. Additionally, fate processes affecting the oil, such as dissolution, photo-oxidation, evaporation and biodegradation are all dependent on the droplet size distribution and its evolution. Accurate transport and fate modelling is crucial for several applications, including response operations, contingency planning and environmental risk assessment. The ambition of the project is to first establish models and experimental tools for studying the small scale. Next, we will derive parameterisations that can be used in large-scale applied oil spill models, based on our experimental work and on existing field data and models for waves. We will then attempt to bridge the gap between the lab and the field scale, through applying our small scale models together with novel 3D simulations of realistic breaking waves. Finally, we will undertake to confirm our model predictions by measuring droplet size distributions under breaking waves in the field, during the annual oil on water exercises conducted in Norway.

Funding scheme:

PETROMAKS2-Stort program petroleum