Abstract: Accurate prediction of absolute permeability remains the central obstacle to efficient depressurization-based production of marine gas-hydrate reservoirs. Here we use pore-scale numerical experiments to quantify how hydraulic tortuosity and absolute permeability co-evolve in hydrate-bearing sediments and to clarify how the microscopic hydrate habit influences the pore-scale flow field. A random-growth algorithm was first employed in 2-D porous media to reproduce the stochastic nucleation and growth of grain-coating, pore-filling and dispersive hydrates; single-phase flow was then solved by the lattice Boltzmann method. The variation trend of tortuosity with increasing hydrate saturation (S_h) is affected by microscopic hydrate habit, but the rise is strongly non-linear for pore-filling hydrates under high nucleation frequency, whereas grain-coating hydrates produce a gentle, almost linear, ascent. Normalized absolute permeability decays significantly with S_h; dispersive hydrates cause the steepest drop at low saturations, whereas grain-coating hydrates exhibit the slowest decline. The microscopic hydrate habit thus governs the coupled evolution of tortuosity and permeability: pore-filling hydrates accelerate the loss of permeability by simultaneously lengthening flow paths and blocking pore throats. The results unveil the morphologically controlled interplay between hydrate occurrence and pore structure, providing a theoretical basis for permeability evaluation and production optimization of gas-hydrate reservoirs.