Study on the Micromorphology and Rheology of Tetrahydrofuran Hydrate during Formation and Dissociation Processes

Clarifying the flow properties of hydrate slurries is of paramount importance for flow assurance in oil and gas pipelines and the application of hydrate technologies. In this study, the formation and dissociation processes of tetrahydrofuran (THF) hydrate at different concentrations and temperatures were observed by a visualized rheometer for the first time, and the influence of the micromorphology of THF hydrate on its rheology was discussed. Otherwise, observations indicate that under shear conditions, the morphology of THF hydrates transforms from nearly 2D plate-like crystals to 3D aggregates, accompanied by a sharp increase in the viscosity of the THF hydrate slurry. The results show that both temperature and concentration impact the crystal morphology of THF hydrates, thereby affecting the rheological properties of the hydrate slurry. Higher temperatures result in smaller aggregate volumes and lower peak viscosities, making the hydrate aggregates more prone to fragmentation under flow conditions. Conversely, higher concentrations lead to greater peak viscosities, with aggregate volumes initially increasing and then decreasing, making the aggregates more resistant to breakage at a concentration of 30 wt %. Compared to temperature, THF concentration exerts a more significant influence on the morphology and rheological properties of hydrates. Additionally, by observing the dissociation process of THF hydrates under static conditions, two primary states of hydrate dissociation were identified, both of which generate a large number of bubbles toward the end of the dissociation process.