Experimental Study on the Morphology and Memory Effect of Methane Hydrate Reformation

The memory effect of hydrate reformation has an important influence on the hydrate growth mechanism and technological applications. This paper focuses on the relation between the morphologies and memory effects of hydrate reformation and the stability of the memory effect using a visual research method. The results indicated that the hydrate morphology differed between the first formation and the reformation. A specific flocculated hydrate was observed only in the process of hydrate reformation. Moreover, the flocculated hydrate was unstable, and it was observed to first grow and then shrink. In this study, the free water was observed to also become turbid during hydrate dissociation. In addition, many gaps were generated during hydrate dissociation, which affected the hydrate dissociation efficiency and the geological safety of hydrate exploitation. The effects of the dissociation temperature and pressure difference on the stability of the memory effects were investigated. The results showed that the memory effect tended to be stable in the closed and heating dissociation patterns. Furthermore, depressurization significantly inhibited the memory effect of hydrate reformation. After depressurization, the induction time of first hydrate formation was increased 4-fold compared with the induction time before depressurization. The experimental results are well explained by the mechanism of dissolved gas remaining in solution after hydrate dissociation.