# Numerical Simulation of Oil Pipeline Leakage Diffusion in Dashagou Yellow River Crossing Section
## 1 Introduction  
With the rapid development of the economy, oil has become the main energy and raw material for all walks of life [1], occupying an important position in the development of the national economy. It is key to the petroleum and petrochemical industry coping with the high-quality and high-speed development of the country [2] and is an important strategic resource. However, in the process of oil production, transportation and storage, especially in oil exploitation areas and petrochemical product production areas, leakage accidents occur frequently, resulting in soil pollution. In recent years, petroleum hydrocarbon pollution has gradually become one of the main forms of soil pollution in the petroleum and petrochemical industry [3, 4]. After oil leakage, it migrates to the soil under the action of gravity and capillary force. Once it enters the environment, it will undergo physical migration processes, such as volatilization and convection-dispersion, and chemical migration processes, such as adsorption-desorption, dissolution and precipitation in the soil [5, 6], which will not only destroy the original structure of the soil but also change the physical and chemical properties of the soil, reduce soil permeability and affect the growth of microorganisms [7]. In addition, the leaked oil very easily penetrates into the groundwater through precipitation, surface runoff and other ways [8], causing pollution to the groundwater, having a serious impact on animals and plants and greatly increasing the mortality rate. In addition, the oil volatilized into the air will be ingested by the human body through breathing, skin contact, diet and other ways, which will affect thenormal function of liver, kidney and other organs to varying degrees and even cause cancer, teratogenicity and mutagenicity, causing great harm to the human body [9; 10; 11]. Under the action of water circulation, the atmosphere will cause serious pollution, and a part of the evaporated substance will fall to the ground and deposit after chemical changes. Every year, about 8 million tons of oil in the world will enter the environment through various ways, such as running, bubbling, dripping and leaking [12; 13], while about 600,000 tons of oil in China, of which about 70,000 tons will flow into the soil, causing pollution to China's ecological environment [14; 15]. In 2004, thousands of tons of crude oil leaked from a pipeline in Yan'an, Shaanxi Province, polluting hundreds of acres of farmland [16; 17]. In 2015, the oil spill of Changqing oilfield polluted tens of kilometers of river, causing serious soil pollution in Wuqi County, Yan'an City. The list of soil pollution risk control and remediation of Beijing-Tianjin-Hebei construction land shows that chemical pollution sites account for 44.1%, among which petroleum hydrocarbon, one of the main pollutants, accounts for 42.10% [18]. According to the investigation and statistics of Russian scientists, 7% of the global crude oil extraction will enter the environment every year and then pollute the soil and groundwater [19]. It can be seen that the harm caused by oil leakage has a huge impact on animals and plants and the ecological environment. In recent years, soil restoration and ecological environment management have received extensive attention. The existing soil remediation technologies include physical remediation, chemical remediation and biological remediation. However, due to the complex structure and properties of petroleum, these remediation technologies all have certain limitations [20]. Up to now, the remediation technologies of oil-contaminated soil are still being improved [21; 22]. There are many such oil pipeline leakage events, so it is very important to study oil pipeline leakage.