Soil-water characteristic curve and permeability of hydrate-bearing soils

Understanding the soil-water characteristic curve (SWCC) and permeability of hydrate-bearing soils plays a critical role in analyzing the production efficiency and layer stability during hydrate exploitation. Based on the self-improved apparatus, hydrate is formed within clayey silt and sand sediment, and the SWCC of the hydrate-bearing clayey silt and sand is measured. Further, the influence law and mechanism of hydrate formation on the SWCC are investigated, and the permeability of the hydrate-bearing soils at unsaturated state is analyzed. The test results show the hydrate formation has a significant effect on the SWCC of the hydrate-bearing soils. As the hydrate saturation increases, the boundary effect segment remarkably increases, the SWCC changes gently during the transition segment, and the corresponding saturation reduces. However, the VG model is able to address the SWCC of the hydrate-bearing soils. Since the hydrate formation changes the pore-size distribution structure of the hydrate-bearing soils, the gas entry pressure increases but the saturation of the effective residual water decreases with the increasing hydrate saturation. Under the unsaturated state, the relative permeability of the hydrate-bearing soils reduces with the increasing capillary suction as the seepage channel is crowded by gas. At a given capillary suction, the higher hydrate saturation corresponds to the smaller relative permeability.