Laboratory investigation of oil viscosity effect during carbonated water injection: Comparison of secondary and tertiary recovery

The performance of carbonated water injection (CWI) with different oil viscosities and rock wettability was investigated through two main series of high-pressure core flooding experiments on both clean and aged sand. The results obtained demonstrated that the capability of carbonated water to enhance oil recovery for both secondary and tertiary flooding was substantially greater compared to water flooding. The creation of a low resistance flow channel and low oil recovery in water flooding was compensated for by CO₂ diffusion and subsequent viscosity reduction and oil swelling in heavy and light oils. The results of the aged sand experiments showed that changing the wettability towards mixed wet caused ultimate reduction in oil recovery in each experiment, compared to the similar one in clean sand. The amount of oil recovered after breakthrough increased compared to that in clean sand, which showed the capacity of CW for enhanced oil recovery through alteration of wettability.