Simulation Study of the Influence of Wettability on CO2 Solubility Trapping Based on the Experimental Fluid Phase Distribution

Solubility trapping is a permanent trapping mechanism that reduces the distance traveled by the plume and increases the amount of CO2 stored. The degree of fluid wetting of the rock determines the distribution of the fluid phase in the pore space, which in turn affects CO2 capillary trapping and dissolution trapping. In this paper, a CO2 dissolution simulation method based on the real fluid phase distribution is established. Firstly, the fluid distribution grid model was constructed based on the real fluid phase distribution obtained from CT experiments. Subsequently, the dissolution-diffusion processes of CO2 in water-wet and oil-wet conditions were simulated by the Volume of Fluid (VOF) method and the Compressive Continuum Species Transfer (C-CST) method. It is shown that the spatial distribution and microgeometry of CO2 are different in different wetting conditions, which in turn affects the dissolution trapping ability of CO2. The specific surface area of CO2 clusters determines the dissolution kinetics. In oil-wet condition, CO2 saturation decreases at a higher rate, and CO2 has a higher mass dissolved percentage and a greater ability to dissolve. In the early stage of dissolution, CO2 concentration increases rapidly, showing a high dissolution rate. During the dissolution process, CO2 clusters split, and the specific surface area of CO2 clusters gradually increases. The specific surface area of CO2 in contact with other fluids (SW-N) gradually decreases, and SW-N shows a good linear relationship with CO2 saturation. Our results show that in a oil-gas-water three-phase fluid system, the solubility trapping of CO2 is more favorable when the porous medium is oil-wet.