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Abstract Carbon dioxide flooding offers dual benefits of enhanced oil recovery and greenhouse gas storage, with strong potential in unconventional reservoirs. However, the nanoporous nature of these reservoirs introduces strong wall–fluid interactions and confinement effects that substantially alter fluid thermodynamics. As a result, the conventional Peng–Robinson equation of state shows noticeable deviations when predicting phase behavior at the micro- and nanoscale. This study reviews advances in understanding CO2–crude oil systems in nanopores, highlighting critical property shifts, phase envelope deformation, and the reduction of minimum miscibility pressure (MMP). Most existing approaches apply single-mechanism corrections and lack integrated models that couple multiple confinement effects. To address this gap, we developed a dimensionless correlation linking critical properties to pore size, derived from experimental and molecular simulation data. This correlation was combined with adsorption layer thickness adjustment, capillary pressure, and volume translation to construct a modified EOS. The model was applied to multicomponent flash calculations and the multiple-mixing-cell method to predict MMP under nanoconfinement. Validation demonstrated high accuracy and robustness across pore sizes, compositions, and temperatures. Results indicate that critical temperature and pressure decrease nonlinearly with pore size, with pronounced changes below 10 nm. The phase envelope shifts toward lower pressures and temperatures, while the two-phase region contracts. The MMP decreases significantly with pore size reduction. These findings reveal the coupled mechanisms governing CO2 flooding behavior in unconventional reservoirs and provide theoretical support for optimizing injection strategies and evaluating storage potential.