Formation of Methane Hydrates from Super-compressed Water and Methane Mixtures

Abstract

AbstractUnderstanding the high-pressure kinetics associated with the formation of methane hydrates is critical to the practical use of the most abundant energy resource on earth. In this study, we have studied, for the first time, the compression rate dependence on the formation of methane hydrates under pressures, using dynamic-Diamond Anvil Cell (d-DAC) coupled with a high-speed microphotography and a confocal micro-Raman spectroscopy. The time-resolved optical images and Raman spectra indicate that the pressure-induced formation of methane hydrate depends on the compression rate and the peak pressure. At the compression rate of around 5 to 10 GPa/s, methane hydrate phase II (MH-II) forms from super-compressed water within the stability field of ice VI between 0.9 GPa and 2.0 GPa. This is due to a relatively slow rate of the hydrate formation below 0.9 GPa and a relatively fast rate of the water solidification above 2.0 GPa. The fact that methane hydrate forms from super-compressed water underscores a diffusion-controlled growth, which accelerates with pressure because of the enhanced miscibility between methane and super-compressed water.