Devolopment of MRI-monitoring method to obtain the map of gas-storage ratio in gas-hydrate mash and MRI observation of Time-evolution maps of gas-storage ratio in hydrate formation process

Utilization of gas-hydrates as a gas-storage medium has a possibility of highly economical transport and safety storage of natural gas. Based on the idea, a development of industrial techniques for high-rate formation of gas-hydrates with high gas-storage ratio is required. In order to improve the method to form gas-hydrate mash with high-storage ratio, a new method for monitoring gas-storage ratio map in gas-hydrate mash by magnetic resonance imaging (MRI) was developed. In this study, gas-hydrate mash was formed from HFC-32 and water in the nonmagnetic high-pressure vessel with fine-bubble injection and mixing paddles, and MR images of gas-hydrate mash were obtained using a portable MR microscope. At a same time, fluid motion of a hydrate mash mixed by the paddle was also observed through the vessel with transparence glass-cylinder using optical camera. The spin-lattice relaxation time, T1, and the spin-spin relaxation time, T2, of a uniform mixing hydrate mash were obtained quantitatively as a function of the gas-storage ratio, which is defined as the ratio of the net gas-volume including in a gas-hydrate mash to the water volume in the vessel. It was obtained experimentally that both relaxation times T1 and T2 did not change from the relaxation times of distilled water before gas-hydrate formation. Based on the results, it was shown that a linear relationship is established between the NMR signal intensity from gas-hydrate mash and the gas-storage ratio in it the derived equation agress to the experimental result measured by gas-hydrate mash mixed uniformly by the paddle. Using the equation, the maps of the gas-storage ratio in a hydrate mash can be quantitatively calculated from MR images. This method was applied to the non-uniform measurement of the gas-storage ratio formed in the gas-hydrate mash under non-uniformly mixing condition. The formation mechanism of the gas-hydrate mash with non-uniform ratio was discussed from the obtained maps of gas-storage ratio and the observation of fluid motion using optical method.