Objective Hydrate slurry transportation offers an effective way to save on reagent costs and is expected to be utilized as a safe, economical, and efficient mode for transporting natural gas through submarine pipelines. Current research is primarily focused on experimental studies related to hydrate formation in defined shapes and the rheological properties of hydrate slurry. Conversely, there have been few studies conducted on the spontaneous crystallization of hydrate slurry and crystallization under flow shear. Nonetheless, crystallization is one of the key factors influencing the rheological properties of hydrate slurry. Studying the crystal growth of hydrates in slurry aids in analyzing and predicting flow conditions within submarine pipelines, which is essential for ensuring the safe flow through these pipelines.

Methods First, the theoretical analysis of the spontaneous crystallization process of tetrahydrofuran (THF) hydrates was conducted, and the results were subsequently verified through a polarizing microscopy experiment. Following this, a high-precision rheometer was employed to investigate variations in crystal growth characteristics under dynamic shearing, alongside exploring the impact of shear rates, cooling rates, and other factors on the rheological properties of hydrate slurry.

Results The static in-situ THF hydrates exhibited growth into rod-shaped crystals, with axial growth rates surpassing radial growth rates. The shear effect induced higher quantities of THF hydrate crystallization, leading to reduced single crystal sizes and a transition in shape from rods to blocks. The viscosity of the slurry showcased an exponential decrease with increasing shear rates, initially rising sharply before stabilizing as the cooling rates of the flow system increased, and surging with higher THF mass fractions.

Conclusion The smaller interfacial energy and greater temperature gradient at the ends of rod-shaped crystals of THF hydrates enhance axial growth. On the contrary, shear effects contribute significantly to altering intercrystalline orientations, leading to the transformation of rod-shaped crystal clusters into blocky crystals. These findings can serve as valuable references for future studies focusing on hydrate formation in flow systems and hydrate slurry transportation.