# Microscopic Experiments to Assess the Macroscopic Sweep Characteristics of Carbon Dioxide Flooding
## 2 Research Methods
### Experimental Devices and Samples  
In this study, considering the non-homogeneous stratigraphic characteristics of reservoirs in CO\({}_{2}\)-driven target blocks in the study area, a two-layer, two-dimensional visual large-object model was designed to conduct two-dimensional visual experiments of CO\({}_{2}\) mixed-phase flooding. The experiments involve the visualization of CO\({}_{2}\) microscopic waves and features using a glass-etched object model and the visualization of CO\({}_{2}\) macroscopic waves and features using a two-dimensional visual large-object model [14].  
Wet-etching equipment, ICP etching machines, and optical and electron microscopes were primarily used to create the glass etching object models. In the glass wet-etching process, a hydrofluoric acid (HF) solution is used to etch the glass surface. The key parameters include the concentration of the HF solution, the temperature, and the etching time. Before etching, the glass substrate surface is polished and coated with a protective mask, followed by a coating of photoresist and pre-treatments such as baking, exposure, and development. The etching solution removes the exposed film layer within the pattern, after which the substrate undergoes cleaning and hardening to prepare for the final etching treatment. An apparatus for performing high-precision etching using an ICP (inductively coupled plasma) etching machine includes a power supply generated by upper and lower electrodes. The upper electrode is responsible for dissociating the gas into plasma, while the lower electrode serves as a support for the substrate and also plays a role in controlling the pressure within the etching chamber. The plasma created by the upper electrode interacts with the gas and the substrate, facilitating the etching process. The lower electrode helps maintain the desired pressure conditions necessary for precise etching. To observe the surface morphology after etching, an optical microscope can be used to inspect the photoresist pattern, and a scanning electron microscope (SEM) can be used to examine the detailed surface features of the etched glass [15].  
The experimental setup for the two-dimensional visual large-object model consists of five main components: the drive replacement system, the two-dimensional visual large-object model itself, a high-speed camera, a back pressure controller, and a fluid metering system. We utilized a high-pressure precision displacement pump, the Chandler Quizix QX5210, for the drive replacement system. The two-dimensional visual large-object model had a visual area of 170 \(\times\) 150 mm, with a maximum working pressure of 22 MPa and a working temperature of up to 110 \({}^{\circ}\)C. Distilled water served as the pressure transfer medium, and non-mercury piston pressurization was used to apply pressure to the test fluid. The flow chart of the two-dimensional visualization experiment device is shown in Figure 1[16].  
Figure 1: Flow chart of two-dimensional visual experimental device.  
In this study, crude oil from the target block of the CO2 flooding in the Lunnan oilfield was selected, and the experiments utilized glass materials to create a granular-filled microscopic model to visualize the drive process in the porous medium and to analyze the morphology of the microscopic residual oil and its formation mechanism. The crude oil samples were prepared by mixing ground, degassed oil, aviation paraffin, and C2-C5 components in a specific ratio. The purity of the CO2 injection gas samples was 99.95%.