Beschreibung:
The feasibility of enhancing CO2 storage using an N2 alternating CO2 (NAC) injection scheme in water-flooded oil reservoirs was investigated. Core flooding experiments of NAC and continuous CO2 injection were conducted. The solubility of CO2 and N2 in water and oil was considered using experimental data, Henry's law, and PR equation to assess the dynamic storage of CO2 during gas injection. The results indicate that N2 slugs in NAC process can significantly reduce gas mobility in comparison with continuous CO2 injection, which is beneficial to increase gas sweeping efficiency in oil reservoirs by inhibiting the formation of predominant gas channels, and thus providing more space for CO2 storage. The numerical simulation using a field scale model shows that, compared with continuous CO2 injection, the gas flooding front of NAC is broader and more regular. The gas swept area can be increased by over 25.2%. Optimization of the NAC process was also performed using a model combining the surrogate model and the particle swarm algorithm. By optimizing the number of N2 slugs, the injection time, and the amount of N2 injection, the NAC scheme can enhance CO2 storage by 11.2% and oil production by 24.3% compared with continuous CO2 injection