With the technical progress in carbon dioxide （CO ₂） flooding for enhanced oil recovery （CO ₂-EOR），it is of great significance to study the influence mechanism of CO₂ injection on the viscosity of crude oil. This study systematically investigated the synergistic effects of temperature （20-40 ℃），pressure （0.5-3.5 MPa），and water content （0%-60%） on the viscosity of saturated CO ₂   dissolved gas crude oil through laboratory experiments. The results showed that under constant pressure，for every 5℃ increase in temperature，the viscosity decreases by approximately 60%-80%. At a constant temperature，for every 0.5 MPa increase in pressure，the viscosity decreases by approximately 1%-5%. In terms of water content，a 10% increase in water content leads to a rise in viscosity by 15%-50% before the inverted point （water content < 40%）. After the inverted point （water content>40%），for every 10% increase in water content，the viscosity decreases by 50%-80%. Based on the experimental data，the prediction performance of three classic models，namely Standing，Glaso and Vazquez & Beggs （V&B），was evaluated. It was found that the V&B model had the best robustness. The XGBoost algorithm combined with Bayesian optimization was used to dynamically correct the V&B model，and a multi-parameter mapping relationship of temperature，pressure and water content was established. The average relative error of the model was reduced from 20.1% to 6.9%，and the average absolute error was decreased by approximately 66%. This study provides a theoretical basis and intelligent prediction tool for the process design and dynamic optimization of oil and gas gathering and transportation systems under CO₂ flooding conditions.

In the process of CO₂ flooding production and oil lifting，with the decrease of pressure，a large amount of associated gas will be separated from the produced liquid. In the associated gas，the content of CO₂ is as high as 50%-90%. Compared with CH₄，gaseous CO₂ has a stronger throttling cooling effect，which may cause the generation of hydrate to block the pipeline，threatening the operation safety of the gathering and transportation system. The influence of CO₂ content on the CO₂-CH₄ gas throttling and hydrate generation characteristics was studied using a high-pressure sapphire reactor. The results show that：When the initial pressure is high （16 MPa），the throttling effect coefficient D_i of the mixture gas with the same CO₂ proportion is about 1.3-5.4 ℃/MPa，and the incorporation of CH₄ will enhance the throttling effect of the mixture gas，indicating that the high pressure section is mainly affected by the throttling effect of CH₄；when the initial pressure is low （5 MPa，4 MPa），the throttling effect coefficient D_i is about 3.4-11.9 ℃/MPa，and the incorporation of CH₄ will weaken the throttling effect of the mixture gas，indicating that the low pressure section is mainly affected by the throttling effect of gaseous CO₂. The higher the pressure at which CO₂-CH₄ gases with the same CO₂ content are，the higher the temperature at which hydrates are generated，and the easier it is to generate hydrates. At the same pressure，the lower the CO₂ content is，the lower the temperature at which hydrates are formed. When the CO₂ content is 8%-100% and the pressure is 1.5-5 MPa，the hydrate generation temperature is 0.5~10 ℃. The comparison results between the experimental and software simulation data show that the PR equation of state has a high correlation for the calculation of CO₂-CH₄ throttling and hydrate generation characteristics. The research results can provide a reference for the selection of safe gathering and transportation process parameters.

Gas-liquid separation for the produced fluid of CO2 flooding is an important step in the process of carbon capture，utilization and storage（CCUS），and its efficiency directly affects subsequent crude oil dehydration，associated gas processing，produced water treatment，as well as the selection and operation life of related equipment. Based on the basic composition of the produced fluid，the impact of CO2 on the properties of associated gas，oil and produced water is stated，and the main impacting factors and mechanism of oil foaming and associated gas desorption are analyzed. And then，a solution for efficient separation of gas and liquid is put forward，main methods and application effect of gas-liquid separation are reviewed，and the direction and trend for future study on gas-liquid separation are pointed out. The results show that the relationship between the pressure reduction rate and the foaming characteristics of oil is the key scientific problem to determine the pressure and stage number for gas-liquid separation. Establishing a prediction model for the relationship between oil foam volume and defoaming time under the synergistic effect of multiple factors is helpful to determining the separation time. The organic combination of ultrasonic desorption technology and mechanical separation technology is expected to form a new cost-effective and efficient gas-liquid separation technology