Effect of salinity on the formation of methane hydrate in unconsolidated sediments

In-depth understanding of the characteristics of methane hydrate formation in unconsolidated sediments containing saline solution is of great significance for the accurate evaluation of hydrate resources in marine sediments. In this study, the effect of salinity on the formation characteristics of methane hydrate in unconsolidated sand samples was studied using the low-field nuclear magnetic resonance in-situ detection technology. Results show that there were differences in the induction time of hydrate formation in pores of different sizes in the unconsolidated sands; methane hydrate was more likely to form in small pores. As the salinity of pore water increased, the induction time of hydrate formation increased exponentially. In the first 20 minutes, the hydrate formation rate first increased and then decreased, and the formation rate was the highest under the salinity of 3.0 wt%. At different locations of the unconsolidated sediments, the difference in the induction time of methane hydrate formation and the mode change of water through the hydrate film caused changes in the hydrate formation rate. The large potential energy on sediment surface and the barrier effect caused by the presence of hydrates prevented some pore water in the samples from being converted into hydrates. The increase in the initial salinity of pore water could enhance the barrier effect, decrease the final conversion rate of pore water, and reduce the hydrate saturation.