The influence of inhomogeneous hydrate formation on permeability anisotropy of porous media

Hydrate formation is an inhomogeneous process, which results in permeability anisotropy, i.e., permeability differs in different directions. Permeability anisotropy of hydrate-bearing sands is analyzed based on CT (computed tomography) scanning and pore network modeling in this study. A digital sample is divided into eight different parts based on hydrate distribution. Eight equivalent micropore structures are extracted by the maximum ball method. The absolute and relative permeabilities of each part in three different directions (x, y, and z) are calculated by a permeability simulator. Before hydrate formation, the sand pack permeability in the different directions is nearly the same. After hydrate formation, the sample pore structures become more complex. Both the absolute and relative permeabilities vary in the different directions. When hydrate saturation exceeds a threshold, the degree of permeability anisotropy is weakened. Hydrate formation induces a more significant relative gas permeability anisotropy compared to relative water permeability anisotropy. The degree of relative water permeability anisotropy increases at high water saturations.