# Numerical Simulation of Oil Pipeline Leakage Diffusion in Dashagou Yellow River Crossing Section
## 4 Results and Discussion
### 24 h Simulation Results and Analysis  
Considering that the flow time of the simulated flow pattern does not exceed 1 h in the above simulation, the 24 h leakage flow pattern simulation is carried out in this project to provide a certain reference to deal with the oil leakage in the pipeline in the crossing section when the pipeline leakage occurs but fails to trigger the pipeline monitoring system due to the small leakage port, slow flow rate and small pressure change in the pipeline. The 24 h  
Figure 19: Histogram of apparent velocity comparison of all simulated flow modes in Dashagou crossing section pipeline.  
leakage flow simulation is only for the pipeline leakage scenario in the layer of pulverized sandy soil (sandy silt) with high resistance in the crossing section of the Dashagou. It is assumed that the buried depth of the pipeline is 12 m, the soil around the pipeline is saturated, the radius of the leakage opening is 20 mm, and the leakage opening is located directly below the pipeline, i.e., at the bottom.  
The simulation results of the 24 h long-time leakage flow pattern in the crossing section of the Dashagou are shown in Figures 20 and 21, and the comparison of the characteristic lengths and apparent velocities of the leakage flow pattern at different moments are shown in Figure 22.  
Figure 21: Schematic diagram of comparison of simulation results of Dashagou crossing section for 24 consecutive hours (view of pipeline section).  
Figure 20: Comparison of 24 h continuous simulation results of Dashagou crossing section (side view of pipeline).  
Combined with Figures 20-22, it can be seen that the buried depth of the pipeline is 12 m, the soil around the pipeline is saturated, the radius of the leakage port is 20 mm, the leakage port is located directly under the pipeline, the leakage flux in 24 h ranges from 0.131678 kg/s to 0.0131656 kg/s, and the rate of change in the leakage flux over time is not significant, which is about 0.1316 kg/s. The total amount of leakage in 24 h is 5670.22 kg, i.e., about 5.67 tons, and the affected soil volume is 22.19 m\({}^{3}\). The total amount of leakage in 24 h was 5670.22 kg, i.e., about 5.67 tons, and the volume of affected soil was 22.19 m\({}^{3}\). The maximum distance of leakage diffusion in 24 h appeared in the vertical direction, which indicated that the trend of oil leakage was mainly downward; according to the simulation results of 24 h, the maximum distance of oil diffusion in the vertical direction was about 8.14 m, the range of diffusion in the lateral direction was 21.99 m\({}^{2}\) in 24 h, and it could be seen that the range of diffusion in the lateral direction was not significant. The range of lateral diffusion is 21.99 m\({}^{2}\) in 24 h, from which can be seen that the range of lateral diffusion is not significant. Considering that the distance of vertical diffusion is larger, it can be inferred that the main trend of oil leakage in the Dashagou area is vertical downward transport and diffusion. The apparent flow rate of oil leakage is gradually decaying, the volume of soil affected by the leakage is 22.19 m\({}^{3}\) in 24 h, the oil leakage is 5.67 tons, and the apparent flow rate of \(Z\)-axis is 0.34 m/h. Due to the resistance of the sandy chalk layer, the apparent flow rate is 1 cm/h after 14 h of leakage, and the flow is stable for a long period of time.