Multi-scale simulation of relative permeability of pore network in tight reservoir with boundary slip and wettability effect

In unconventional reservoirs, micron- to nanometer-scale pores are widely distributed, leading to molecular interactions at the solid–liquid interface and immobile boundary layers along the pore walls. To elucidate the mechanisms by which boundary layer effects and adsorption behavior influence fluid migration in pores, this study develops an enhanced pore network model (PNM) that incorporates both boundary layer effects and oil-phase adsorption. This enables integration of multi-scale simulation approaches. Molecular dynamics (MD) simulations were conducted to investigate the density and velocity distributions of water and model oil which based on saturates, aromatics, resins, and asphaltenes classification, within water-wet and oil-wet nanopores of varying sizes and wettability conditions. The results show good agreement with a modified Hagen–Poiseuille equation, validating the model. From the MD simulations, an empirical relationship between slip length and pore size was derived and well-fitted, quantitatively capturing how wettability transitions affect slip behavior. Using pore structure data obtained from actual core samples, a realistic PNM was constructed. By integrating the empirical slip-length function, nanoscale slip corrections were introduced into the model, enabling the calculation of phase-specific relative permeabilities. Comparison between the model predictions and experimental data demonstrates that accounting for slip effects significantly improves the agreement with measured relative permeability curves, thereby enhancing prediction accuracy. Overall, this study comprehensively characterizes fluid adsorption, slip, and transport behavior in micro- and nanopores through a cross-scale simulation framework. These findings provide novel insights and technical support for understanding fluid migration in unconventional reservoirs and for optimizing numerical simulation methods.