# Microscopic Experiments to Assess the Macroscopic Sweep Characteristics of Carbon Dioxide Flooding
## 4 Conclusions  
The Lunnan oilfield in the Tarim Basin is in the late stage of double-layer water flooding development, characterized by highly dispersed remaining oil reservoirs and a complex reservoir environment, making the improvement of oil recovery a challenging task. This study focuses on the TI reservoir in the No. 2 well area of the Lunnan oilfield in the Tarim Basin. Through the analysis of the geological characteristics of the Lunnan oilfield in the Tarim Basin, we observed the real-time interaction process between carbon dioxide and crude oil using transparent microscopic models and high-resolution imaging technologies. We visually simulated the microscopic waves and characteristics of carbon dioxide using glass etching models and simulated the development scenarios of the oilfield  
Figure 8: Variation curves of recovery degree and oil production rate under different HCPV split injection and combined recovery conditions. under various injection-production combinations using two-dimensional visual large-scale physical models. Based on these models, we conducted CO2 miscible flooding experiments under different injection-production modes, comparing the microscopic and macroscopic waveforms and characteristics of CO2 flooding, as well as the oil displacement efficiency under various injection-production modes. Our findings provide valuable data supporting the physical authenticity of the microscopic and macroscopic waveforms and characteristics of CO2 flooding in the Lunnan oilfield of the Tarim Basin. The main findings are summarized as follows:  
1. Carbon dioxide flooding in non-homogeneous reservoirs: The target block reservoirs exhibit non-homogeneous stratigraphic characteristics. Two-dimensional visual experiments were conducted based on a glass etched object model to investigate the microscopic waves and characteristics of CO2 flooding. During water flooding, water is predominantly found in the large pore throats and pores connected to large pore throats, while the small pore throats and pore spaces controlled by small pore throats, as well as pore blind ends, are difficult to drain, leaving residual oil primarily in the form of small pore channel retention and adsorption on the wall surface. CO2 flooding is primarily a mixed-phase driving with crude oil, characterized by strong component exchange and pore filling. At the late stage of the driving, the oil film on the wall surface can be desorbed. The microscopic driving efficiency approaches 100%, and with an increasing CO2 pore volume multiplier, the crude oil in the pore blind ends can be cleanly displaced. Supercritical CO2 enters the blind-end pore space through component exchange and mass transfer, mobilizing a large amount of residual oil. 2. Macroscopic waves and characteristics of CO2 flooding: Three groups of two-dimensional visual physical simulation experiments were designed based on the distribution position of the isolation layer and the physical properties of T12 and T13. For the isolation layer located at the injection and production ends, combined injection-production and split injection-production methods were used to simulate the conditions. Under the strong non-homogeneity of the Lunnan 2 TI reservoir, different injection and production modes lead to noticeable differences in the mixed-phase wave characteristics and displacement effects between the two layers with permeability gradient differences. These differences directly impact the utilization of reservoir suction capacity, gravitational anisotropy, density differences, and the control effect of the isolation layer. The differences in the development effects of various injection and production modes are more closely related to the control effect of the isolation layer. In summary, this study employed advanced transparent microscopic models, high-resolution imaging, and two-dimensional visual large-scale physical simulations to analyze the micro- and macro-characteristics of CO2 flooding.