# Microscopic Experiments to Assess the Macroscopic Sweep Characteristics of Carbon Dioxide Flooding
## 3 Experimental Results
### Macroscopical Sweep Characteristics of Carbon Dioxide Flooding  
Figures 5 and 6 show the images and curves related to the carbon dioxide (CO\({}_{2}\)) oil displacement process under conditions of co-injection and co-production with different hydrocarbon pore volume doubling rates (HCPVs) of injected hydrocarbons. Figure 5: Images of CO\({}_{2}\) oil flooding process under co-injection and co-production with different injected hydrocarbon pore volume multiplication rates. Co-Injection and Co-Production:  
As depicted in Figure 5, when the upper and lower layers were co-injected with an isolation fluid and the lower layers far from the isolation fluid are produced, the total recovery rate was 52.83%. The process was dominated by flooding, with a weak miscibility effect. The inhalation ability is positively correlated with the permeability, leading to distinct differences in reservoir drive effects. A notable phenomenon of non-injection and non-extraction occurred in T12, which contrasted significantly with the T13 flooding [21]. Figure 7 illustrates the curves of the recovery degree and the oil recovery rate under different HCPV co-injection and co-production conditions. It can be observed that as the HCPV increased, the recovery degree initially rose rapidly before slowing down, with a critical HCPV of 0.5. The oil production rate initially increased in a wave-like pattern, then rapidly decreased, and subsequently declined more gradually. The HCPV at the TI gas breakthrough point was 0.5. The TI gas breakthrough indicates the point at which gas begins to break through into the production wells, marking a significant change in the flow dynamics and recovery efficiency [22]. Separate Injection and Combined Production:  
Figure 5 also depicts the CO\({}_{2}\) oil displacement process under separate injection and combined production with different pore volume doubling rates of injected hydrocarbons. The upper and lower layers were simultaneously injected with isolation fluid, while production occurred away from the lower layer. Considering the differences in physical properties, T12 was injected first, followed by T13, creating a dual effect of gravitational differentiation and spacer influence on fluid transport. This significantly affected the behavior of both the T12 and T13 layers, allowing CO\({}_{2}\) to further reduce residual oil and effectively displace the mixed-phase zone, achieving a total recovery rate of up to 88.68% [23]. Figure 6: Change curves of recovery degree and oil production rate under different HCPV co-injection and co-production conditions. Figure 8 displays the curves of the recovery degree and the oil recovery rate under different HCPV separate injection and combined production conditions. With increasing HCPV, the recovery degree initially rose rapidly before slowing down, with a critical HCPV of 6.5. The oil production rate exhibited a wave-like increase, followed by a rapid decline, a subsequent rapid increase, and finally a gradual decline. The HCPV at the TI gas breakthrough point was 0.63, and the HCPV at the injection and recovery transformation point was 6.5. This is primarily due to the increased injection rate accelerating the diffusion of hydrocarbons within the pore space. Once the pore space is fully saturated with hydrocarbons, the development and production efficiencies improve, but further increases in the injection rate have minimal impact on recovery degree and oil recovery speed. \"Suction capacity\" refers to the capacity of the reservoir to absorb fluid. It is positively correlated with permeability, which means that, the higher the permeability, the stronger the inhalation ability. This is important because it affects the distribution and displacement of fluid in the reservoir. Co-Injection and Co-Production with Different HCPVs:  
Figure 5 provides images of the CO\({}_{2}\) oil displacement process under co-injection and co-production with varying pore volume doubling rates of injected hydrocarbons.