• A fractal-based permeability model for rough fracture networks accurately predicts single-phase and two-phase flow with deviations under 10%.
• Fracture number, tortuosity, and aperture are the dominant geometric parameters controlling permeability.
• Flow regimes significantly influence relative permeability in gas-water two-phase systems.
• The framework offers a practical, physically based method for analyzing multiphase seepage in fractured rock, applicable to field-scale systems.