Hydrate Particle Evolution and Slurry Flow Behavior in Deepwater Subsea Pipelines

Hydrate formation in deepwater subsea pipelines is a critical flow assurance problem during offshore oil and gas production and transportation. The generation, aggregation, and transport of hydrate particles can progressively change slurry behavior and increase the risk of local blockage. To clarify the evolution of hydrate particles under flowing conditions, experiments were conducted in a high-pressure flow loop using in situ microscopy, high-speed imaging, and particle image velocimetry (PIV). The evolution of crystal morphology, particle velocity field, and vorticity structure was systematically analyzed during hydrate formation. Two distinct types of hydrate crystals were identified: irregular opaque fragments originating from interfacial hydrate film breakup, and transparent clustered particles formed through bulk-phase nucleation and aggregation. PIV analysis shows that the average particle velocity exhibits a non-monotonic trend with increasing water conversion fraction ( WCF ), initially increasing and subsequently decreasing. Analysis of the particle-based vorticity reveals that hydrate formation progressively modifies the flow structure. Based on these observations, a four-stage flow evolution model is proposed to describe the transition from dispersed particle motion to cluster-dominated hydrate slurry transport. The results provide useful insight into hydrate slurry evolution and transport behavior in deepwater subsea pipelines.