Study on CO2 Flooding Crude Oil Production Characteristics and Factors Affecting Oil Flooding Efficiency in Tight Reservoirs

To clarify the influence mechanism of micronano pore-throat development characteristics on CO₂ flooding efficiency and crude oil mobility degree in Block X of tight oil reservoirs, this study combined a long-consolidated tube model in the core flooding method to determine the MMP, utilizing high-pressure mercury injection and nuclear magnetic resonance technologies to conduct CO₂ immiscible and miscible flooding experiments on three types of reservoir cores; quantitative analysis addressed the recovery factor, pore-throat scale crude oil mobilization characteristics, and flooding efficiency-influencing factors, with experimental results indicating first that CO₂ immiscible flooding achieved optimal efficiency in Class III reservoirs at a 60.4% recovery, showing significant mobilization in macropores and mesopores but critically low mobilization at 28.9% in micropores and 11.5% in nanopores; second that CO₂ miscible flooding demonstrated a peak efficiency of 71.3% in Class II reservoirs, significantly enhancing mobilization to 40.2% in micropores and 16.7% in nanopores while achieving near-complete mobilization approaching 100% in macropores and mesopores; third that the pore-throat radius exhibits a significant negative correlation with CO₂ immiscible flooding efficiency, with its impact substantially stronger than on miscible flooding, where mechanistic analysis confirms the pore-throat structure as the key controlling factor for CO₂ flooding efficiency with critical synergistic pressure effects, establishing superior suitability of lower-pressure immiscible flooding for Class III reservoirs versus distinct advantages of miscible flooding in better connected Class II reservoirs, thereby providing practical guidance for enhanced oil recovery technologies in tight oil reservoirs.