Unlocking residual oil after CO₂ flooding: The role of tributyl citrate as a solvent-based mobilizing agent

CO₂ flooding in light-oil reservoirs can induce compositional redistribution and heavy-fraction deposition, leading to pore-structure deterioration, permeability reduction, and limited oil recovery. Although tributyl citrate (TBC) is a promising solvent-type additive for improving oil fluidity and CO₂–oil compatibility, its role in remobilizing residual oil affected by deposition remains insufficiently under-stood. This study integrates visual interfacial observations and PVT measurements with core-flooding tests and multiscale characterization to elucidate CO₂–oil interaction-driven deposition and the TBC-assisted remobilization process. Results show that CO₂ preferentially extracts light hydrocarbons (C₁–C₉) while enriching intermediate (C₁₀–C₂₉) and heavy components (C₃₀₊), thereby destabilizing crude-oil colloidal structures and promoting irreversible deposition. In homogeneous cores, miscible CO₂flooding at 20 MPa achieves a high recovery of 77.08% but also induces 15.28% heavy-component deposition and up to 38.23% permeability reduction. In contrast, fractured cores exhibit less deposition but markedly lower sweep efficiency. The addition of TBC mitigates these adverse effects by suppressing viscosity growth, enhancing CO₂ solubility and oil swelling, and improving CO₂–oil compatibility. These synergistic effects strengthen interfacial mass transfer and provide an additional 13%–18% recovery enhancement beyond CO₂ flooding alone. Multiscale observations suggest that TBC reduces the aggregation tendency of deposited heavy components and improves pore-scale flow continuity. These findings provide insight into the remobilization of deposition-affected residual oil after CO₂ flooding and demonstrate the potential of TBC to mitigate formation damage and enhance CO₂-EOR performance in light-oil reservoirs.