Investigation of hydrate formation and flow characteristics within multiphase transmission pipelines employing a constant pressure visualization loop system

Hydrate blockages during oil and gas transportation severely affect flow safety. An innovative, fully visual flow loop was utilized to systematically evaluate and quantify the individual effects of pressure, temperature, flow velocity, and liquid loading on hydrate formation, flow characteristics, and morphological evolution. The results indicate that hydrate growth progresses through the stages of initial formation, slurry stable flow, and aggregation and blocking, with the water conversion fraction and differential pressure exhibiting pronounced stage-dependent evolution features. Increased pressure augments the fugacity gradient, thereby reducing the hydrate formation time and blocking time, exacerbating particle aggregation, and facilitating hydrate generation. At constant pressure, high subcooling accelerates gas consumption and lengthens hydrate formation time, promoting the development of microporous aggregate network structures. The water conversion fraction increases with subcooling but remains insensitive to variations in subcooling during the blocking stage. A critical flow velocity exists, above which hydrate can continue to be transported in suspension in the main pipeline, although deadlegs remain susceptible to blockage. Furthermore, flow velocities exceeding 0.27 m/s can postpone blockage when below the critical threshold. High liquid loading delays hydrate formation time but shortens blocking time, and the maximum water conversion fraction occurs at a liquid loading of 60 vol%. During the slurry stable flow stage, hydrate conversion above this critical value is governed by particle aggregation and continued hydrate formation. These experimental findings advance the understanding of hydrate behavior in multiphase flow systems under constant pressure, providing a foundation for improving risk assessment and flow assurance strategies.