Affecting Mechanism of Natural Sandstone Porous Media on the Formation and Phase Equilibrium of Methane Hydrate

Gas hydrate in sandstones constitutes a significant component of hydrate resources within the Qilian Mountain permafrost region in China, which has a great significance of investigating the affecting mechanism of the natural sandstone porous media on the formation and phase equilibrium of methane hydrates. With a self-designed apparatus employed, hydrate formation experiments were conducted utilizing natural sandstone as the porous media. The equilibrium data of methane hydrates in these natural porous media were measured, and the reliability of the obtained data was verified through cyclic experiments. By comparison of the equilibrium behavior of methane hydrate in sandstone porous media to that in pure water, the impact of sandstone on the hydrate formation was determined. Various microscopic tests on sandstone were also conducted to reveal its affecting mechanism on the formation of methane hydrates. The experimental results demonstrate that the sandstone porous media effectively enhance the formation of methane hydrate because of the low specific pore volume, medium pore size, complex pore structure, and diverse phase compositions of the sandstone itself. In sandstone porous media, the equilibrium temperature of methane hydrate is observed to be higher compared to that in pure water at the same pressure. Additionally, the impact of sandstone porous media on methane hydrate equilibrium tends to become more obvious in high-pressure regions. The study also reveals that sandstone porous media, even with a lower specific pore volume compared to artificial porous media, exhibit a similar or even better promotion effect on methane hydrate formation.