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As oil and/or gas exploration and production enter deeper water, the flow assurance confronts challenges, one of which is the hydrate formation and blockage. Investigations about gas hydrate formation and hydrate slurry flow in a multiphase transportation system were performed on a newly constructed high-pressure experimental loop. On the basis of the experimental hydrate formation data, an inward and outward hydrate shell model was improved to predict the gas consumed amount during the hydrate formation process. With the help of a focused beam reflectance measurement and particle video microscope installed in this flow loop, the distribution of hydrate particles was observed, characterized in the coalescence and fragmentation. A “minimum safety flow rate” was first addressed for the safety of hydrate slurry flow in a multiphase transportation system. Then, the comparisons between our experimental data of the natural gas hydrate slurry flow pattern and the Mandhane flow pattern map revealed the influence of hydrate particles on the flow pattern of the slurry. Furthermore, the influence of the gas/liquid superficial velocity on the pressure drop was discussed at stratified flow for this gas hydrate slurry multiphase system.

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Pipeline blockage caused by hydrates and wax in subsea pipelines is a major hazard for flow assurance in the petroleum industry. When hydrates and wax coexist in a flow system, the plugging risk is more severe. The effects of wax on hydrate formation, agglomeration process, flow properties, and plugging mechanisms were studied in a high-pressure flow loop using water-in-oil (w/o) emulsion systems. The flow properties of the system with the presence of wax were entirely different from those of the system without wax under the same experimental conditions. Three types of plugging were observed in the flow loop: rapid plugging, transition plugging, and gradual plugging. The interaction relationships between wax crystals, water droplets, and hydrate particles and the formation of wax−hydrate aggregates were proposed based on the particle video measurement (PVM) probe observation and the analysis of the fluid viscosity. The mechanisms of different plugging scenarios were presented, which were highly correlated with the temperature and initial flow rate. The presence of wax would impact on the agglomeration process of hydrate particles leading to a catastrophic decrease in the transportation ability and an extremely high plugging risk after hydrate formation in the pipeline.

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