Formation characteristics of THF hydrate within media under a temperature gradient detected by multi-layer NMR
Abstract
<p indent="0mm">In nature, ground temperature proportionally varies with depth. The formation characteristics of hydrate within sediments under temperature gradient present an important reference value for the application of hydrate as a resource or technology. Using multi-layer nuclear magnetic resonance, the formation processes of tetrahydrofuran (THF) hydrate within silica gel powder containing different contents of solution was detected under a temperature gradient for the first time. The results showed that the formation processes present obvious heterogeneity in the vertical direction due to the temperature gradient. The difference in the contents of solution is responsible for the heterogeneity. Furthermore, the formation rates and the final conversions of THF hydrate were both significantly higher in the medium with higher contents of solution (<italic>W</italic><sub>silica gel</sub>/<italic>W</italic><sub>solution</sub> = 1:1.5). The average size of the hydrate particles formed within the segment of sample with higher subcooling degree might be smaller, but the final conversion of THF is the lowest. While the content of solution is lower (<italic>W</italic><sub>silica gel</sub>/<italic>W</italic><sub>solution</sub> = 1:1), the subcooling degree present positive correlation with the final THF conversion within the different segments of the sample. However, when the content of solution is higher, the solution is mainly confined in the large-size pores of medium. As a result, the formed solid hydrate can become new skeletons of medium. Therefore, the distribution of particles can be changed and the medium gradation optimized. Similarly, the distribution configuration and the law of liquid in media can also be affected. On the contrary, the skeleton structure of medium will not be affected within the media with lower content of solution.</p>
