Effects of morphology of trapped CO2 bubbles on dissolution mass transfer in porous media: A pore-scale simulation

Understanding CO2 dissolution in porous media is crucial for assessing the efficiency and safety of geological carbon storage. While empirical power-law correlations can capture the effect of flow velocity on mass transfer, they often overlook the influence of bubble morphology. In this study, we employ pore-scale direct numerical simulations to investigate the dissolution process of trapped CO2 bubbles in porous media with two typical configurations: singlets and clusters. Key transport parameters, including interfacial area, flow field distribution, local Péclet number, and concentration distribution, were analyzed under different flow rates and saturations to evaluate performance. Results reveal a non-monotonic trend in mass transfer coefficients for singlet bubbles with increasing saturation—initially rising and then declining. At low saturations (<10%), increased gas–liquid interfacial area and enhanced pore-scale water velocity strengthen convective transport and promote dissolution. In contrast, at high saturations (>15%), the development of extensive stagnant flow regions suppresses local concentration gradients, resulting in diffusion-dominated transport and reduced overall mass transfer rate. A comparison between bubble morphologies shows that singlet bubbles dissolve significantly faster than clusters, not only due to greater interfacial area but also higher overall mass transfer coefficients. Moreover, for singlet bubbles, a consistent power-law relationship between Sherwood and Reynolds numbers is observed across all conditions, with the scaling exponent strongly depending the gas saturation and bubble configuration. These findings emphasize the critical role of bubble morphology in CO2 dissolution and provide quantitative data for improving continuum-scale reservoir models.