多层核磁探测介质内温度梯度下THF水合物形成特征

Formation characteristics of THF hydrate within media under a temperature gradient detected by multi-layer NMR

自然条件下,地温会随深度呈比例变化.温度梯度下沉积物内水合物形成特征,对水合物资源及技术应用具有重要参考意义.本文运用多层核磁共振仪,对不同溶液含量硅胶粉内温度梯度下四氢呋喃(THF)水合物形成过程进行探测.结果显示:温度梯度使形成过程在垂向上呈明显异质性;水(溶液)含量差异是引起形成过程差异的主要原因.此外,溶液含量较高时(W硅胶/W溶液=1:1.5),介质内水合物形成速率及THF最终转化率明显较高,试样内,由处在较高过冷度状态下的溶液形成的水合物颗粒平均粒径较小,但THF最终转化率最低.溶液含量较低时(W硅胶/W溶液=1:1),过冷度与试样段内THF最终转化率呈正相关关系.然而,含量较高时,溶液主要滞留于大尺寸孔隙中,此时形成的固态水合物可成为新骨架,改变介质颗粒分布,优化颗粒级配,影响液体的分布形态及规律.相反情况下,水合物对介质骨架结构无影响.

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(Wsilica gel/Wsolution=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(Wsilica gel/Wsolution=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.