Abstract: The easily precipitation of aphaltine from crude oil during the CO2 displacement results in the decreasing of permeability，wettablity alteration，the damage of the layer and reduction of gas injection recovery efficiency.This article focuses on the condition and mechanism of asphaltine precipitation and harm during the process of CO2 miscible flooding in the case study of oil reservoir of Taizhou Group in Caoshe Oilfield.After the discussion of the thermodynamic relationship between the parameters of CO2 injection and asphaltene precipitation，it can be concluded that the front of asphaltine deposition is in accordance with the front of gas injection，most of the asphaltine near the bubble point pressure on the injection side deposits and the amount of asphaltene precipitation is much more in the condition of low differential-pressure displacement than the high differential-pressure displacement.According to the relationship between the second liquid phase and asphaltine precipitation characterized by the phase diagram of P-X，the phase model predicting asphaltine precipitation during the process of the oil multi-contacting with gas is established and the asphaltine precipitation near the well-bore zones can be reduced in the condition of lower CO2 injection pressure and higher differential-pressure displacement or injecting solvent similar to aromatic hydrocarbon.The increasing of oil production by CO2 displacement is improved.

Key words: Caoshe Oilfield, CO2 displacement, miscible flooding, asphaltine precipitation, deposit mechanism, displacement pressure