Nanoconfined multi-phase interactions govern distinct phase behavior of CO₂-oil in shale during CCUS-EOR process

Nanopores are widely distributed in shale oil formations, and the distinctions induced by nanoconfinement significantly affect the accuracy of multiphase fluid behavior prediction and flow characterization during CCUS-EOR process. While it has been established that fluid-wall interactions, fluid adsorption and capillary pressure strongly influence the CO₂-oil physical properties, most existing studies only focus on a limited combination of such factors. Particularly, wettability is frequently overlooked in the majority of investigations, leading to substantial deviations from true phase behavior and limiting model reliability. Addressing the limitations in current works, we introduce a new critical property shift model coupled with an equilibrium calculation framework based on the modified Peng-Robinson equation of state (PR-EOS) to comprehensively account for these effects. Our results demonstrate that critical properties including saturation pressure, density, and minimum miscible pressure (MMP) decrease as pore size reduces below 75 nm, and gradually approach bulk values for larger pores. Concurrently, capillary pressure increases with the gas-liquid contact angle, enhancing liquid-phase enrichment of light components and consequently decreasing density and saturation pressure. Wettability further alters phase envelope by lowering bubble and upper dew point pressures, raising the lower dew point, and narrowing the two-phase region, while the critical point and MMP remain unchanged. These findings deepen the understanding of nanoconfined fluid flow behavior and provide fundamental knowledge for advancing CCUS-EOR in shale.