Investigation of Oil Production with Different CO2 Injection Methods at Microscale and Macroscale

This research employed micro- and macroscale experiments combined with numerical simulation to investigate oil production using different CO2 flooding methods. Microscale experiments visualized oil displacement via various CO2 immiscible flooding techniques. Water-alternating-gas (WAG) and foam flooding left less residual oil compared with continuous CO2 flooding. Macroscale experiments compared immiscible and miscible flooding, revealing that miscible displacement increased oil recovery by 28% compared with immiscible displacement. Subsequently, WAG, form, and continuous CO2 flooding experiments were conducted at a water-flooded oil reservoir. Compared with continuous CO2 flooding, WAG and foam flooding enhance oil recovery by 5.49% and 5.43%, respectively. Numerical simulation was used in the field-scale case study. It shows that the minimum miscible pressure (MMP) of the reservoir was 23.7 MPa. The optimization injection rate was 9,696 m3/day/well, and production rate was 13 m3/day/well in continuous CO2 flooding, yielding a cumulative oil production of 171.89×104 m3 after 20 years. The optimization ratio of the CO2 slug to water slug was 2∶1 in WAG flooding. After 20 years, the cumulative oil production was 175.606×104 m3, 4×104 m3 more than continuous CO2 flooding. WAG flooding also enhanced CO2 storage ratio by 6.83%. This study provides valuable experimental data relevant to CO2 flooding and storage in water-flooded oil reservoirs.