Lattice Boltzmann modelling of molecular interaction governing multiphase flow in nanoporous media

Understanding multiphase flow in nanoconfined spaces is essential for a wide range of scientific and engineering applications. In these systems, strong fluid–fluid and fluid–solid molecular interactions induce non-negligible nanoscale effects, resulting in complicated and poorly understood non-Darcy flow behaviours, thereby rendering many existing conventional pore-scale simulation methods inadequate. In this work, a nanoscale pseudopotential lattice Boltzmann model incorporating molecular interactions that give rise to wall slip, interfacial slip and heterogeneous viscosity, is developed to investigate the underlying mechanisms of molecular interactions governing multiphase flow in nanoporous media. The theoretical solutions of single-phase and two-phase flow in nanopores are first analysed based on the Hagen–Poiseuille equation, and the lattice Boltzmann model is then validated for accuracy and used to obtain microscopic parameters through molecular simulations and theoretical analysis. The proposed model is then applied to simulate the displacement of the non-wetting phase by the wetting phase, systematically examining both the individual and coupled effects of molecular interactions, initial wetting-phase saturation, wettability and capillary number on displacement behaviour, patterns, efficiency and phase trapping in nanoporous media. A universal scaling relationship is identified between the flow enhancement factor and displacement efficiency, with nanoscale effects transitioning from flow enhancement to suppression as displacement efficiency increases. These simulations and findings elucidate how fluid–fluid and fluid–solid molecular interactions govern multiphase transport in nanoporous media.