CO₂ diffusion and dispersion in porous media: review of advances in experimental measurements and mathematical models

CO₂ molecular diffusion in subsurface porous media is one of the key mechanisms in high-pressure–high-temperature CO₂ geosequestration and CO₂-based enhanced oil recovery projects. The mass transfer rate of injected supercritical CO₂ and its dissolution in reservoir fluids are mainly described by the gas diffusion coefficient. Over the past decades, numerous efforts have been made to investigate the CO₂ molecular diffusion process in both hydrocarbon reservoirs and saline aquifers. However, various experimental methods and mathematical models with simplified assumptions were used to determine the CO₂ diffusivity, which sometimes led to inaccurate or contradicting results. Hence, it is essential to critically review and compare the CO₂-diffusion-related literature for better application in geoscience, chemical, and petroleum engineering fields. In this review, we critically review the physics of CO₂ diffusion in porous and nanoporous media, including the diffusion theory, factors affecting the CO₂ diffusion coefficient in hydrocarbon reservoirs and saline aquifers, analysis of laboratory measurement methods, their advantages and disadvantages and limitations, and also evaluation of previously developed mathematical models and their uncertainties and empirical correlations, in detail. Additionally, we briefly discuss CO₂ dispersion in porous media from various aspects. Finally, potential research areas related to CO₂ diffusion in porous media are proposed.