Modelling tortuous pathways of H2 and CO2 in organic microstructures for improved gas migration prediction

Abstract

This study investigates the crucial challenge of precisely modeling how hydrogen and carbon dioxide move and spread within the tight confinement of organic-rich rock formations. This is especially important for understanding potential gas distribution and ensuring the secure containment of these gases during geo-storage operations, where injected gases like hydrogen or carbon dioxide could migrate through the complex network of organic microstructures in source rocks. By combining Grand Canonical Monte Carlo simulations for sorption analysis and molecular dynamics for diffusion assessment, this research offers a comprehensive approach to understanding gas behavior in these complex systems. The study involved constructing kerogen models with varying microporosity (13.7%–32.9%) to delineate the impact of pore structure on gas diffusivity and establish tortuosity-porosity relationships for hydrogen and carbon dioxide. Results demonstrate significantly higher sorption capacity for carbon dioxide (2.5–6 times) compared to hydrogen due to stronger gas-kerogen interactions. Consequently, carbon dioxide exhibits markedly lower diffusivity (20–52 times) compared to hydrogen. Moreover, the study reveals distinct tortuosity values, within the same structures, for hydrogen (ranging from 1.1 to 2.29) and carbon dioxide (ranging from 2.92 to 4.15), emphasizing the influence of gas-specific properties on transport behavior within organic-rich formations. These findings contribute to a more accurate representation of gas transport processes in these complex environments and provide valuable insights for optimizing geo-storage strategies.