Flow characteristics of CO2 hydrate-containing fluids in nanopores: Insights from molecular dynamics

The flow of mixed fluids with CO2 hydrates in nanopores critically affects CO2 sequestration, enhanced oil recovery, and gas transport. To clarify the effects of varying CO2 hydrate saturation on the flow behavior of fluids in nanopores, this study uses molecular dynamics simulations to examine how varying hydrate saturation influences fluid behavior in nanopores. The simulations cover fluid behavior at different CO2 hydrate saturations (0.0%–28.57%), with a focus on analyzing changes in mass density distribution, potential energy, radial distribution function, mean square displacement (MSD), CO2 diffusion coefficients, hydrogen bonding, hydrate cage structures, fluid–wall interactions, velocity distributions, and flow behavior within the pores. The results show that with increasing CO2 hydrate saturation, the diffusion capacity of CO2 molecules in nanopores decreases, as reflected by reduced slopes and magnitudes of MSD curves. The highest CO2 diffusion occurs at 0% saturation, while a significant slowdown is observed at 28.57%. Meanwhile, the hydrogen bond network strengthens and hydrate cage structures evolve, limiting the mobility of both H2O and CO2 molecules. Fluid–wall interactions also intensify with higher saturation, requiring greater force for fluid displacement. Velocity profiles become flatter with reduced peak velocities, indicating diminished fluid mobility. Mass flux analysis reveals that hydrate formation severely restricts the flow of water and CO2, leading to a progressive decline in relative permeability. These findings provide important insights into CO2 hydrate transport in nanopores and offer theoretical guidance for optimizing gas capture and storage technologies.