Formation and Blockage Mechanisms of NGH in Deepwater Undulating Pipelines under Multiple Factors

To mitigate severe risks posed by hydrate blockages in deepwater oil and gas operations, this study investigates the formation and blockage mechanisms of natural gas hydrate (NGH) in undulating subsea pipelines. Through large-scale flow experiments, we quantitatively analyzed the impacts of subcooling, the gas–liquid ratio, and the pipeline inclination angle. Key findings reveal that increased subcooling markedly accelerates hydrate formation, reducing the blockage time to approximately 97 min at 6 K subcooling. Although a high gas–liquid ratio (6000:1) promotes hydrate generation, stronger hydrodynamic shear under such conditions delays particle deposition, extending full blockage time to around 150 min. Furthermore, steeper inclinations significantly elevate the blockage risk, with the 60° inclined pipe exhibiting the earliest blockage. This study provides some references for researching the deposition patterns of hydrate formation in complex pipelines and theoretical guidance for flow assurance in deepwater operations.