Characteristics and Influencing Factors of Crude Oil Mobilization in Different Microscopic Pores During Supercritical CO₂ Flooding in Tight Oil Reservoirs

Against the backdrop of growing global energy demand and declining conventional oil and gas resources, understanding the mobilization mechanisms of crude oil at the microscopic pore scale in tight reservoirs is critical for efficient development. This study focuses on the tight oil reservoirs of the Yanchang Formation in the Ordos Basin. By employing nuclear magnetic resonance (NMR) real-time monitoring technology and slim-tube displacement experiments, we established a classification standard for reservoir pore structures and clarified the miscibility characteristics of the CO₂-crude oil system, as well as the oil mobilization behaviors across different reservoir types. The results indicate that the Chang 7 reservoir in the study area can be categorized into Type I, II, and III, with corresponding decreases in pore storage capacity and flow capability. Under immiscible conditions, Type III reservoirs exhibited the highest oil displacement efficiency. Near-miscible and miscible conditions, however, favored Type II reservoirs with optimal displacement performance. These findings provide a theoretical foundation for optimizing CO₂ flooding strategies in tight oil reservoirs, supporting both efficient resource development and carbon neutrality goals.