CO₂ Diffusion and Dispersion in Porous Media: Review of Advances in Experimental Measurements and Mathematical Models

Abstract

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.