The Transport-diffusion Forecast Of The Oil Spill From Seabed Pipeline And Its Application In The Beibu Gulf

In the process of oil transportation with seabed pipeline, petroleum pollutants caused by pipes outburst discharged into the ocean and the water quality condition will be polluted in varying degrees, then it is of highly necessary to study on the leftover of spilled oil from seabed pipeline and scope and extent into the ocean, and provide scientific basis for environmental management and protection in projects'design.This thesis simply introduces the background of this kind of study, and summarizes in details the status-quo of the oil spill model developing at home and abroad. Specific works are listed as follows:1. The barotropic velocity of Beibu Gulf and the nearby sea of Weizhou Island, taken as a basis of background velocity field in the near-field model an input into the far-field substance transportation model, is calculated by Backhaus-3D nonlinear tidal numerical model and verified by comparing with the observation data obtained in six Weizhou on-site observation Stations.2. The near-field buoyant jets model of the oil spill from seabed pipeline was established with Lagrangian integral control cells. The model assessed the influence imposed by spilled oil in near field transport and diffusion processes under different ocean current, flood tide and ebb tide conditions.3. After calculation of the transport and diffusion processes in the near-field, the diffusion by current of spilled oil should be studied through far-field model. Based on the non-linear tidal numerical model, the transportation equations are solved by adopting the random walk method, and a oil spill prediction model is established, the near-field and far-field model are coupled by taking the results of the near-field model as an input to the far-field model, thus leading to a transport and diffusion model for off shore oil spill.4. This model is applied to simulating the the oil spill process around Weizhou 11-4 oil field in Beibu Gulf. The impact of near-field transport and diffusion of oil spill by altering the initial emission angle, how the near-field dilution,the oil mass and cover area in far-field will vary are studied. It's also showed from the results that the impact is very strong in offshore location with different initial emission angle, but the impact by other factors, like the radius of buoyant jets, area and the dilution degree, is slight. The tidal current also influenced in the movement of buoyant jets. In the far-field, oil diffusion area will increase gradually with time in the initial stage of oil spill, and the pollution ocean area will increase obviously. In the evening, the oil diffusion area will drop off until the oil to land.The model is verified. The results of near-field transport and diffusion matches well with the results obtained from the sewage ocean outfall model. In the far field, the simulated results when sources treated as discrete and uninterrupted source are compared, which present us that the movement trend under both circumstances are the same, with the area of spilled oil close, while the instantaneous oil spill area is relatively smaller when treated as discrete source, along with more spilled oil absorbed.This study enriched transport and diffusion forecasting methods of seabed pipeline oil spill and can be taken as a reference when working on the similar study.