Abstract: In order to clarify the mechanism of CO₂ flowing in the nano-pores of shale reservoirs and its influence on asphaltene deposition, a nano-filtration experiment was conducted with self-developed high-temperature and high-pressure filtration vessel and composite nano-filtration membrane to simulate the CO₂ flooding process under the action of single (multi)-layer rock slices, and to study the influence of reservoir parameters and injection parameters on CO₂ flooding effect and asphaltene deposition. The results showed that CO₂ flooding caused asphaltene deposition, resulting in the asphaltene content in the remaining much higher than that in the produced oil; the asphaltene content in the produced oil increased with the increase of CO₂ injection pressure and filter membrane pore size, but decreased with the increase of temperature, shut-in duration, membrane thickness and heterogeneity; the influence degree of reservoir parameters and injection parameters on asphaltene deposition was as follows: membrane thickness (40.63%), injection pressure (20.74%), heterogeneity (16.84%), temperature (10.86%), membrane pore size (7.37%), and shut-in duration (3.56%). The study results provide reference and basis for enhancing the recovery efficiency of shale oil reservoirs by CO₂ flooding.

Key words: CO₂ flooding, shale oil, nano filtration membrane, asphaltene deposition, heterogeneity