Water Permeability Characteristics of Natural Gas Hydrate-Bearing Silty-Clayey Sediments

Over 90% of hydrate reserves are located in marine reservoirs, particularly in low-permeability silty-clayey sediments in the South China Sea (SCS). Understanding the water seepage characteristics of these sediments is vital for the commercial exploitation of hydrates in the region. In this study, a customized experimental platform was used to prepare hydrate-bearing silty-clayey sediments, and steady-state water seepage experiments were conducted under varying hydrate saturation and sediment porosity conditions. Results show that the minimum hydraulic gradient increases with hydrate saturation below 5% but decreases above this threshold. Non-Darcy flow occurs below a hydraulic gradient of 15 × 105, while Darcy flow prevails above it. Permeability initially decreases and then increases with hydrate saturation. For sediments with a porosity of 45%, permeability is reduced to a minimum at a hydrate saturation of 3% and is subsequently increased. Permeability increases significantly with porosity, rising by 140% when porosity increases from 40% to 50% at 20% hydrate saturation. Factors such as the pore state, hydrate blockage, cementation, and preferential flow channels influence permeability. This study provides theoretical support for understanding water seepage in marine hydrate reservoirs.