Molecular Insights into Multiphase Transport through Realistic Kerogen-Based Nanopores

Water is ubiquitous within organic-rich shale in cases of connate water occurrence and during hydraulic fracturing treatment. Understanding multiphase transport behaviors in organic nanopores is crucial for the efficient development of shale gas reservoirs. However, current studies have predominantly focused on single-phase or two-phase transport behaviors in ideal graphite nanopores, leaving the understanding of multiphase transport processes within realistic kerogen-based nanopores limited. In this study, we conducted molecular dynamic simulations to investigate shale gas transport behaviors through organic nanopores constructed with realistic kerogen. The results reveal that, due to the complex composition in the chemistry and physics of kerogen macromolecules, gas transport through kerogen nanopores manifests parabolic-shaped velocity distributions with a negligible slip length at the walls, in contrast to the observations of fast mass transport in previous studies using smooth carbon-based skeleton nanopores. In water-saturated nanopores, H2O molecules tend to aggregate at the walls, forming water clusters, and eventually, a water pillar across the pore can be observed. As a result, a water blockage is formed, while the water film or water bridge dominates in some inorganic minerals. The presence of H2O molecules has a dramatic impact on shale gas transport capacity. On this basis, an analytical model was proposed to quantitatively characterize shale gas transport behaviors under different water saturations. The results demonstrate that the traditional continuous model with no-slip assumption remains applicable because of the rough kerogen surface and hindrance of water clusters, advancing the understanding of multiphase transport behaviors in shale nanopores and exploitation of shale gas reservoirs.