A multi-scale transient multiphase flow model for hydrate particle formation-aggregation-deposition in pipeline

Hydrate blockage critically impacts the safety and efficiency of deep-water oil and gas exploitation. Under low-temperature and high-pressure conditions, hydrates tend to form and disperse as solid particles within the multiphase flow. Hydrate aggregation and deposition are widely recognized as the dominant blockage mechanisms. While few quantitative models exist to describe this entire complex process due to the intricate coupling among hydrate phase-change kinetics, particle agglomeration, deposition, and multiphase fluid interactions. This work proposes a novel multi-scale particle–fluid coupling transient multiphase flow model, comprising one Main-core-model and three Sub-models describing hydrate formation, aggregation, and deposition, respectively. To link micro- and meso -scale particle behaviors to macro-scale flow dynamics, new transport equations for the concentration and average diameter of hydrate particles are introduced to characterize the population effect. By resolving the forces acting on the hydrate aggregates, the critical particle size is derived as a function of multi-scale parameters, from which a log-normal distribution of aggregate size is obtained. The model further predicts deposition probability and layer thickness to quantitatively describe hydrate deposition state in the multiphase system. Comparing with experimental data from a high-pressure flow loop, the model demonstrates exceptional reliability and engineering applicability. Through simulation of a horizontal gas-condensate pipeline, the behaviors of hydrate particle formation, aggregation, and deposition are elucidated and the coupling relationship with multiphase flow is clarified. Thereby, this work advances the fundamental understanding of hydrate blockage and provides a reliable basis for flow assurance control strategies in submarine multiphase pipelines.