Experimental study on the forming process of multi-component gas hydrates in Qilian Mountain permafrost area

Multi-component gas hydrates are widely distributed in the fractured layers of the Qilian Mountain permafrost area. It is of great significance to the study of forming processes of the multi-component gas hydrates and better understanding of the formation mechanism of the natural gas hydrates in the Qilian Mountain area. Copying the gas samples released from the Qilian Mountain gas hydrates, multi-component gas samples were artificially prepared. Based on the visual observations under different temperature-pressure conditions, the formation processes of multi-component gas hydrates were respectively studied in pure water, mine water samples and sediment cores collected from Qilian Mountain hydrate deposit area. Based on the morphological characteristics of the multi-component gas hydrates, the influences of different reaction media (mine water salinities and sediments) on the formation of multi-component gas hydrates are discussed. In the pure water system, the multi-component gas hydrates are formed in various forms, such as pine needle, hair filament and block, which appear preferentially at the gas-liquid interfaces and the vessel wall. Compared to the pure water, the formation induction times of multi-component gas hydrates in the mine water samples collected from Qilian Mountain permafrost area were relatively short, suggesting that the low salinity mine water samples have no obvious inhibition on the hydrate formation processes. The induction time of multi-component gas hydrates formation in the Qilian Mountain cores was shorter and the hydration rate was faster than those in solution systems. It is obvious that, the formation processes of multi-component gas hydrates in the Qilian Mountain media shows a feature of "interface priority ". The fracture surfaces of Qilian Mountain cores and the suspended particles in the mine water samples provide the "third interfaces" besides the gas-liquid interfaces and the vessel wall for the hydration reactions, which effectively accelerate the formation processes of multi-component gas hydrates.