Effect of hydrate nucleation mechanisms and capillarity on permeability reduction in granular media

A model for water permeability reduction in hydrate-bearing sediments is presented by considering capillary effect in hydrate nucleation. Both grain-coating and pore-filling cases are considered. The model is developed from a series of lattice Boltzmann flow simulations. Results show that the permeability decreases quasi-linearly with increasing hydrate saturation during grain-coating nucleation and that the permeability tends to be higher than predicted by previous analytical models in which capillarity is not taken into account. The permeability follows unique reduction curve and is not so sensitive to initial sediment bulk density and grain size distribution. Simulations further show that there is a transition zone at Shyd = 0.3 ~ 0.4 where permeability reduction trend switches from grain-coating model to pore-filling model. Analyses of tortuosity and surface area confirm that the permeability reduction mechanisms result from pore-channel blocking in grain-coating case and pore-size reduction in pore-filling case.