Experimental study on gas channeling during CO2 immiscible flooding for low-permeability oil reservoirs

Key words:  CO₂  immiscible flooding  gas channeling  influence law  enhanced oil recovery

Abstract:

CO₂ injection or flooding is an important method to improve oil recovery from low-permeability reservoirs. However, due to the constraints of reservoir conditions, most CO₂ injection projects in China are operated in an immiscible flooding mode, in which gas channeling has a great effect on oil recovery. In this study, the effect of pressure, temperature, gas injection rate and permeability difference on gas channeling during CO₂ immiscible flooding was investigated experimentally, and of the correspondence of oil recovery and produced gas-oil ratio was analyzed. The experimental results show that, as pressure increases, miscible flooding can be gradually achieved, while CO₂ gas channeling is reduced with better oil displacement efficiency. As temperature increases, the solubility of CO₂ in oil decreases, and the time of gas breakthrough becomes shorter with less oil recovery. Under immiscible flooding conditions, the injection rate and reservoir heterogeneity have a significant impact on gas channeling. With the increase of injection rate and heterogeneity, CO₂ channeling and early breakthrough can occur, resulting in increased produced gas-oil ratio and less oil recovery. The results of this study can provide useful guide lines for the design of CO₂ flooding schemes and control of gas channeling.