Anisotropy analysis of two-phase flow permeability in the multi-stage shear process of hydrate-bearing sediments

Natural gas hydrate is a promising energy resource for the future. However, due to the shallow burial and low-degree of consolidation, hydrate-bearing sediment (HBS) is prone to deform under stress. And this will lead to dynamic changes in reservoir permeability. In this study, the micro-structure of shearing HBS specimen with hydrate saturation of 45.1% under different confining pressures (1, 3 MPa) were obtained by the micro-focus CT, the micro-structure changes and two-phases permeability characteristics evolution were analyzed. The results show that with the increasing axial strain, the absolute permeability increase firstly and decrease. The capillary pressure in vertical direction is always larger than that in horizontal directions. During primary gas flooding and secondary water flooding, the gas-water relative permeability anisotropy of different direction gradually enhances, and reach maximum with the largest axial strain. At low effective confining pressure, the gas-water relative permeability in each direction does not vary with axial strain. At high effective confining pressure, the relative water permeability in each direction decreases with the increase of axial strain, the relative gas permeability in the horizontal direction increases with the increase of axial strain, and the relative gas permeability in the vertical direction has no obvious pattern.