A Pore-Network Simulation Model of Dynamic CO₂ Migration in Organic-Rich Shale Formations

One attractive aspect of CO₂ sequestration in shale formations is the preferential adsorption of CO₂ compared to methane, which may provide enhanced methane production as well as sequestration of carbon dioxide. In this work, a comprehensive theoretical model of CO₂ migration at the pore scale is developed to study CO₂ migration properties in organic-rich shale formations. The proposed model takes into account dynamic competitive adsorption between CO₂ and CH₄, slip-flow effects due to the nanometer range of pore sizes, and pore-size changes due to adsorption. Because of the high pressure and temperature, the injected CO₂ is in supercritical phase. Pore bodies in the shale matrix are irregular in shape, with roughness along pore wall. The structure of pore body affects the amount of surface areas and associated number of adsorption sites, and hence, a shape factor is proposed in this work to consider the irregularity of pore structure in shale matrix. The sorption of CO₂ leads to an apparent retardation of the migration of CO₂, which is quantified in this work. The developed pore-network model is extended to consider the impacts of different spatial distributions of the organic materials within the shale matrix.