A numerical study of subsurface oil spills

This thesis addresses numerical modelling of oil entering the ocean from subsurface sources like drilling well blowouts or pipeline failures. We introduce a single-phase oil model, excluding a gaseous component. We've developed a novel Python-based nearfield plume model where buoyant oil forms a coherent plume with a self-similar structure along vertical uplifting. A key contribution is defining essential plume variables and equations for the coupled water-oil system. The nearfield component is validated using lab-scale and real-scale experiments in the North Sea, including a sensitivity analysis on entrainment coefficients, fitting well with in-situ data. As the plume reaches a terminal level due to loss of momentum and buoyancy from ocean stratification, a farfield stage begins. Here, individual oil droplets disperse via ocean currents and eddy-turbulence. The far-field condition originates from the near-field's final state, where the plume element dissolves into oil parcels. Nearfield oil-water mixture at the terminal level seamlessly connects to horizontal and vertical spreading. The farfield component employs a Lagrangian Particle Tracking model (OceanParcels), incorporating a vertical component into the advection-diffusion problem. Size-dependent buoyancy forms distinct clusters with varying resurfacing times. The newly developed plume model and the farfield model, both Python-based, are unified under UWORM (UnderWater Oil Release Model). They utilize 3D ocean state data from the Copernicus Marine Service (currents velocity, temperature, and salinity fields). Uncertainties in both models are discussed for future work. In the nearfield phase, uncertainties focus on entrainment parameter choices and input ocean data, while ocean currents and stratification affect the terminal level. In the farfield, uncertainties concern the resolution of input ocean currents and eddy diffusivity parameterization. Additionally, droplet size distribution significantly impacts the total volume of oil resurfaced.