Study On Characteristics Of Pipeline Leakage And Oil-gas Diffusion

With the increasing depletion of land resources,people are trying to get more of them from the ocean.In the process of developing offshore oil and gas fields,the subsea pipeline has played an important role in the transport of them.But the hazard of oil-gas leaks from cracks because of the seawater corrosion and other reasons is accompanying in this process as well.The leakage accident not only pose a threat to the environment,but also do harm to human life.Therefore,an accurate understanding of oil-gas leakage and diffusion properties can reduce the difficulty of oil recover,improve the efficiency of oil clean-up,and it has a very important practical significance.Based on the above reasons,this paper discussed the diffusion characteristics of oil leakage and oil-gas leakage underwater.The main work of this paper is as follows:(1)Experimental study on oil leakage underwater is carried out,the results show that the leak hole size has a great influence on the size of oil droplet:In a certain range,the lager the leak hole is,the greater the sizes of oil droplets are.The existing formula for estimating the size of the oil droplet is also verified here,the result shows that the formula can only be used when the Reynolds number of oil droplet is less than 100.Based on the experiments,three different sizes of leak hole is calculated.The results show that the flow coefficient increases with the increases of the size of leak hole,and this phenomenon is explained according to boundary layer theory.At the same time,the other characteristics of the plume are studied: as the experiment proves,the greater the amount of leakage is,the much more time that oil will take to float to water surface.And the amount of leakage can also influence the form of floating plume jets.Moreover,experimental study on the transport process of vertical downward oil spill has been carried,and compared with oil spill upward.(2)Leakage process of oil under hydrostatic is simulated in this paper,the details about transport and diffusion of different moments of spilled oil is analyzed as well.At the same time,entrainment process is explained by velocity contours which is obtained from the simulation.(3)With current considered,oil-gas leak and diffusion process is simulated here.The result shows that due to the pressure difference,the oil would move against the current,becoming of the countercurrent.The comparison results show that the vertical velocity component of oil-gas is not affected by the impact of the current velocity.But the current velocity will greatly influence thediffusion range of pollutant,floating jet inclination angle and intensity of entrainment.(4)Numerical simulation is carried out on the diffusion characteristics of water with different gas content,the result shows that the rate of gas phase in oil-gas has played an important role in the process of oil-gas leakage:The greater the rate of gas is,the faster the oil moves upward.Based on this reason,the leakage with high rate of gas will get less influence caused by the current,so the diffusion area will be small.The greater the rate of gas is,the smaller oil droplets are,and the floating jet inclination angle will increase as well.At the same time,the intensity of entrainment increases with the increasing of rate of gas.