@article{Zhang2026, 
author = {Zhi-Hao Zhang and Ming-Wei Zhao and Zhong-Zheng Xu and Qin-Fang Ding and Yu-Xin Xie and Ying-Nan Wang and Yi-Zheng Zhang and Huan Zhang and Xu-Guang Song},
title = {Unlocking residual oil after CO2 flooding: The role of tributyl citrate as a solvent-based mobilizing agent},
year = {2026},
journal = {Petroleum Science},
volume = {23},
number = {9},
pages = {5788-5799},
keywords = {Tributyl citrate, Residual oil, CO2 flooding, Asphaltene/resin deposition, Solvent effect},
url = {https://www.sciopen.com/article/10.1016/j.petsci.2026.06.033},
doi = {10.1016/j.petsci.2026.06.033},
abstract = {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.}
}