Subcooling Controlled Hydrate Crystal Morphology and Aggregate Structure Coupling in Multiphase Flow

Deepwater high-pressure and low-temperature environments make oil and gas transportation prone to hydrate blockage. Elucidating the formation and blockage evolution of natural gas hydrates is therefore critical for ensuring energy security. Hydrate crystal morphology provides a microscopic basis for understanding blockage formation. However, previous studies have mainly focused on hydrate crystal morphological evolution in static systems. In this study, a visualized flow loop was developed to investigate hydrate crystal morphology under multiphase flow conditions. The results indicate that increasing subcooling leads to smoother, more elongated, and more fragmented hydrate particles with greater morphological irregularity at the microscopic scale. At the macroscopic scale, the rate of hydrate formation in the system exhibits a nonmonotonic relationship with the subcooling. With increasing subcooling, increasingly fragmented blocklike and elongated rodlike hydrate particles form denser aggregation structures, thereby increasing flow resistance and causing a higher blockage differential pressure. Subcooling regulates hydrate crystal morphology, which governs aggregate compactness and ultimately controls flow resistance and blockage behavior. The findings highlight that hydrate blockage risk cannot be assessed solely based on the formation rate but must consider hydrate crystal morphology-induced structural evolution. This work provides new insights into the mitigation of hydrate blockage in deepwater energy transport systems. These findings are applicable under the experimental conditions in this study.