SUPERCRITICAL CO₂ WATER DISPLACEMENTS AND CO₂ CAPILLARY TRAPPING: MICROMODEL EXPERIMENT AND NUMERICAL SIMULATION

The CO₂ capillary trapping is an important scientific issue in geological carbon sequestration, but few researches focus on the trapping mechanism at pore scale under supercritical CO₂ condition. In this study, based on the high-pressure fluids-microscopy-micromodel experimental system, we performed drainage experiment, i.e. supercritical CO₂ displacing water, and imbibition experiment, i.e. water displacing CO₂, under the conditions of 45℃ and 8.5 MPa. The DSLR camera was used to capture pictures of CO₂-water two-phase immiscible flow and the microscopy was used to capture the capillary trapping behavior for the supercritical CO₂ at the pore scale. The computational fluid dynamic method was adopted to simulate the two-phase fluid flow processes. The numerical results are generally in agree-ment with the experimental observations, and further provide three-dimensional geometries on the interface during the drainage-imbibition processes and the trapped supercritical CO₂ droplet/cluster. Finally, the capillary trapping curve, i.e. the relationship between the initial CO₂ saturation and the residual saturation, was obtained from the numerical results, and we made an assessment of the three capillary trapping models, i.e. Land's, Jurauld's and Spiteri's trapping models. A comparison of the models performance indicates that Jurauld's model behaves slightly better than Land's model, whereas Spiteri's model behaves poorly. However, given that Land's model only contains one parameter of clear physical meaning, it is recommended for practical use.