## 4 Experimental Results and Analysis
### Dynamic Occurrence Law of Oil and Gas in Depletion Stage  
#### 4.1.1 Microfluidic Experiment of Porous Carbonate Reservoir  
The porous carbonate reservoir model after being saturated with oil is shown in Figure 5. Adjust the back pressure to simulate the depletion development stage. When the pressure reaches the set pressure, the simulated oil in the model begins to degas. The first degassing area is around the production well and the large pore throat area in the model, as shown in Figure 6. At this time, with pressure propagation, the dissolved gas of the crude oil in the small pore throat region does not escape, but exists in the liquid phase. The gas phase migration of the porous carbonate model is shown in Figure 7. The gas in the large pore throat keeps expanding, merging and migrating. Meanwhile, due to the existence of bubbles in the large pore throat, the pore throat in the area where degassing does not occur is the main migration channel; that is, the small pore throat is the main gas migration channel. When the gas passes through the small pore throat, it provides conditions for the aggregation of gas molecules in the small pore throat; that is, auxiliary gas nucleation. As the volume of the released gas increases, the gas phase in the small pore throat gradually expands, merges and migrates. The degassing area of the porous carbonate model is shown in Figure 8.  
At the end of depletion development, the escaped gas exists in both the large and small pore throats. The remaining oil distribution of the porous carbonate reservoir for exhaustion  
Figure 5: Saturated oil in the pore carbonate model. Figure 8: Expansion of degassing zone in porous carbonate model. Figure 6: Macropore throat degassing in the porous carbonate model. Figure 7: Gas phase migration in porous carbonate model. development is shown in Figure 9. According to threshold segmentation calculation, the displacement efficiency of the microfluidic model of the porous carbonate reservoir in the depletion development stage is 37.80%, as shown in Figure 10.  
1.2 Microfluidic Experiment of Fractured Porous Carbonate Reservoir with Fracture Parallel to Mainstream Line  
The fractured porous carbonate reservoir model after being saturated with oil is shown in Figure 6.0 Adjust the back pressure to simulate the depletion development stage, and the degassing process can be divided into three stages, according to the analysis of the experimental results. In the first stage, when the pressure reaches the set pressure, degassing occurs first near the production well. Because fractures are developed around the well, a large amount of crude oil is degassing first along the fractures, and at the same time, crude oil in the matrix near the fractures is degassed. At this time, the fractures are the main oil-producing and gas-producing channels, as shown in Figure 6.1  
Figure 6.2 Fracture porosity model saturated oil. Figure 6.3 Threshold segmentation of depletion development in pore model. Figure 6.4 Distribution of remaining oil in depletion development with pore type model. In the second stage, the degassing range in the matrix is extended from the near-slit matrix to the large pore throat region in the matrix, as shown in Figure 6.5 In addition, gas migration occurs in the matrix with increasing deaeration, as shown in Figure 6.6  
In the third stage, the gas in the large pore throat keeps expanding, merging and migrating. Meanwhile, due to the existence of bubbles in the large pore throat and serious Jamin effect, the migration channel is mainly the pore throat in the area where degassing does not occur; that is, the small pore throat is the main gas migration channel, as shown in Figure 6.7 This provides conditions for bubble nucleation in the small pore throat region, and degassing occurs in the small pore region, as shown in Figure 6.8  
According to the three stages of gas phase evolution, the degassing sequence of the fractured porous carbonate reservoir is fracture, large pore throat region and small pore throat region.