Microscopic experimental investigation into the effects of silt on gas hydrate formation in sandy marine sediments

Marine gas hydrate reservoirs are rich in fine-grained silt, which substantially affects gas hydrate occurrence patterns and sediment pore characteristics. The presence of silt is a key factor that controls gas production efficiency and sand production behavior during hydrate exploitation. In this study, cryogenic scanning electron microscopy (Cryo-SEM) was used to characterize CO 2 hydrate occurrence morphologies in silt-bearing sediments. Low-field nuclear magnetic resonance (LF-NMR) was further employed to examine how silt grain size influences hydrate formation and effective pore size of sediments. The results show that silt has a pronounced effect on hydrate occurrence. Silt promotes the formation of hydrate clusters and strengthens interparticle cementation. Silt also enlarges the space available for hydrate nucleation and growth, leading to a looser pore-filling structure of hydrates. In addition, silt increases the water–gas contact area in pores, and an appropriate amount of silt enhances the hydrate formation rate. However, the presence of silt significantly reduces the effective pore size of hydrate-bearing sediments (HBS), which is unfavorable for sediment permeability. Compared with the HBS without silt, the injected-water signal intensity under the same pressure difference was reduced by about 50% and 20% for the HBS containing fine silt and coarse silt, respectively, indicating that silt reduces the effective pore size and seepage capacity of HBS. This study clarifies the roles of silt in hydrate formation and pore characteristics of HBS, and provides support for developing efficient exploitation strategies and for assessing operational safety in marine gas hydrate production.