## 3 Results and Discussion
### Distribution of Residual Oil in Heterogeneous Porous Media
#### 3.1.2 Effect of Heterogeneous Porous Media on Residual Oil  
The simulation shows that heterogeneity will affect the distribution of residual oil in the oil displacement process. Figure 4 show the changes in the oil volume fraction in different models in the oil displacement process. In all of the models, as shown in Table 1, the ratio of permeability in high and low permeable areas of chip 4 is the largest (\(k_{high\;permable}/k_{low\;permable}\) = 12.61), and the ratio of permeability in chip 2 is the smallest (\(k_{high\;permable}/k_{low\;permable}\) = 2.25). In addition, the ratio of permeability in chip 1 is \(k_{high\;permable}/k_{low\;permable}\) = 4.45, and the ratio of permeability in chip 3 is \(k_{high\;permable}/k_{low\;permable}\) = 6.37. Chip 1 is consistent with chip 4 (high permeable), chip 2 is consistent with chip 3 (low permeable); chip 1 is consistent with chip 2 (high permeable), chip 3 is consistent with chip 4 (low permeable).  
Chip 1 is composed of large-size, low permeable zone and large throat, high permeable zone, and the permeability ratio of the high permeable zone to the low permeable zone is 4.45. The initial water flow advances smoothly in the upstream of the high permeable zone, and then the water flow evolves along a certain dominant channel. At 0.2 min, the model reaches a quasi-steady state, and the water flow breaks through the outlet to form a dominant channel. In chip 1, the water flow does not break through the low permeable zone.  
Chip 2 is composed of a large particle size, low permeable zone and a small throat, high permeable zone. The ratio of permeability of the high permeable zone to the low permeable zone is 2.25. The chip 2 is the chip with the smallest permeability ratio in the four groups of models. Compared with chip 1, the time for chip 2 to form the dominant channel is slower than that of chip 1, and there are still residual oil droplets in the high permeable zone after 1 min. In the later stage, the water phase at the front end of the inlet tends to migrate to the low permeable zone.  
Chip 3 is composed of a small particle size, low permeable zone and a small throat, high permeable zone. The ratio of permeability of high permeable zone to low permeable zone is 6.73. At 0.2 min, the flow begins to enter the front of the low permeable zone, and at the same time, the dominant channel is formed in the high permeable zone. When the breakthrough time is faster than that of chip 1 and chip 2, 1 min, there are residual oil droplets in the high permeable zone, and the water phase has entered the low permeable zone.  
Chip 4 model is composed of a large throat, high permeable area and a small particle size, low permeable area. The ratio of permeability of the chip 4 high permeable area to low permeable area is 12.61, which is the largest in the four groups of models. The predominant channel area distribution of chip 1 and chip 2 is similar, the dominant channel formation time is greater than chip 3, 1 min after the water into the low permeable area.  
Figure 5 is the curve of residual oil in high and low permeable zones in heterogeneous porous media. From the figure, the residual oil in low permeable zone is much higher than that in the high permeable zone under arbitrary simulation conditions. From the simulation results, the residual oil in high permeable zone of large throat (chip 1 and chip 4) is higher than that in the high permeable zone of small throat (chip 2 and chip 3). This is because, in