## 4 Experimental Results and Analysis
### Law of Water-Driven Oil and Gas Mobilization in Water-flood Development Stage  
#### 4.2.1 Microfluidic Experiment of Porous Carbonate Reservoir  
After the porous carbonate reservoir model changes from depletion development to waterflooding development, the injection water preferentially selects the large pore throat containing only simulated oil as the flow channel in the early stage of displacement. This displacement process shows an obvious characteristic of \"displace the oil, not the gas\". This is due to the large flow resistance of gas in the pore throat and the serious Jamin effect. There is a great difference on the waterflooding front between the early displacement stage and the waterflooding stage when the pressure is higher than saturated pressure. The waterflooding front of the waterflooding model is channeling seriously along the large pores, without the stage of advancing as a 1/4 arc, as shown in Figure 20. When water-breakthrough happens, the waterflooding results of the model are shown in Figure 21, and the sweep coefficient is only 0.14.  
As water is injected to restore the formation pressure, as shown in Figure 22, the released gas dissolves and water drive mobilization increases. Figure 23 shows the distribution of the remaining oil in the porous carbonate reservoir model after depletion and water injection. According to threshold segmentation calculation, the oil displacement efficiency of the microfluidic model of the porous carbonate reservoir after depletion and water injection development is 88.82%, as shown in Figure 24.  
Figure 21: Porosity model water in production well.  
Figure 20: Pore model in the early stage of waterflood development.  
2.2 Microfluidic Experiment of Fractured Porous Carbonate Reservoir with Fractures Parallel to Mainstream Line  
After the fractured porous carbonate reservoir model with fractures parallel to the mainstream line changes from depletion development to waterflooding development, the injected water first flows along the fracture at the early stage of displacement, as shown in Figure 25, and then water breakthrough happens quickly and the water cut increases rapidly, as shown in Figure 26. Although the injected water flows through the fracture, the injected water can restore formation pressure in the main line area, and dissolved gas from the main line area gradually dissolves again. When the pores containing only simulated oil increase gradually, the fractured porous model is the same as the porous carbonate reservoir model. The large pore throat containing only simulated oil is selected as the flow channel at the same time, the displacement process shows an obvious characteristic of \" displace the oil, not the gas\", and the water driving range is significantly increased.  
As the water is injected, the formation pressure is restored, and the dissolved gas continues to dissolve. The area where re-dissolution occurs gradually expands from the main line to the edge, and the efficiency of waterflooding increases, as shown in Figure 27. Figure 28 shows the distribution of the remaining oil of the fractured porous carbonate  
Figure 23: Distribution of remaining oil after water injection after initial depletion in pore model.  
Figure 22: Formation pressure recovery in pore model.