Pore-Scale Numerical Study on Permeability Variation of Hydrate-Bearing Sediments Caused by Heterogeneity

Pore habits and distribution heterogeneity of gas hydrates are two microscopic determinants of the permeability of hydrate-bearing sediments. We conducted pore-scale numerical simulations under various saturations to investigate the dependence of permeability on the pore habits, grain coating (GC) or pore filling (PF), and heterogeneity. In our study, the heterogeneity was simplified to the number density of gas hydrate particles under constant saturation: more particles correspond to less heterogeneity. Permeability positively correlated with heterogeneity for the GC habit, while no correlation was observed for the PF habit. We assumed that the permeability was controlled by two values: the critical width, which is the widest width of the narrowest points of multiple flow paths, and the number of wide flow paths. A pore network model was constructed to validate this assumption based on pore body and throat radius frequency distribution, average coordination number, and percolation paths. Network analysis showed that the permeability–heterogeneity correlation for the GC gas hydrate was caused by pore space constriction, not blocking, and connectivity reduction. We suggest that future research should focus on the time dependence of distribution heterogeneity at the sediment scale.