Pore-Scale Investigation into the Effects of Fluid Perturbation During Hydrate Formation

In order to increase the gas production efficiency during methane hydrate exploitation, the research focus should be nowadays on the methane hydrate formation and decomposition mechanisms. As methane hydrate reformation and the hydrate heterogeneity in the pores of sediments show great influence on gas production during hydrate decomposition, new insights need to be supplemented to reveal the mechanism of the hydrate phase transition. In this work, a new microfluidic chip 'simple straight pipe chip' was designed based on the microfluidic device. By comparing it with the former chip 'cylindrical structure chip,' a series of experiments were conducted to investigate the morphology of the hydrate phase transition. The 'water perturbation under a gas-filled situation' method and the 'gas perturbation under a water-filled situation' method were applied for hydrate formation. The results connect different methane hydrate growth patterns to different occurrence patterns in hydrate-bearing sediments. In the gas-filled situation, with the water migration rate rising, the hydrate stable state varies from a grain-coating hydrate to a load-bearing hydrate. In the water-filled situation, with the gas migration rate rising, the stable hydrate state becomes narrower. These results also gave explanations for hydrate reformation and heterogeneity in hydrate-bearing sediments. The depressurization in gas production will create water and gas flow to varying degrees, which will lead to hydrate reformation and the heterogeneity situation. Finally, these findings also provided valuable information and data for gas production and further research into gas hydrate.