Objective Pipelines with undulating profiles are susceptible to liquid accumulation at low-lying positions along their route, particularly when utilized for gathering and transmission of wet natural gas and transmission of oil-gas blends. Considering the significant difference in inclination angle between gathering and transmission pipelines and gas wells, foam drainage technology, already wellestablished for the removal of liquid accumulation from gas wells, needs to be further demonstrated before its application to transmission pipelines carrying oil-gas blends.

Methods Gas-liquid multiphase pipe flow experiments were conducted using an experimental loop setup, aimed at investigating the impact of foam on the characteristics of gas-liquid multiphase flow at various inclination angles and elucidating the mechanism of plug formation in foam-containing multiphase flow. Additionally, the study examined the impact of changes in foam system properties induced by the presence of inorganic salts on the characteristics of foam-containing multiphase flow. Flow regime-specific analysis was conducted on flow characteristic parameters and pressure difference features.

Results In pipelines with undulating profiles and significantly different inclination angles compared to gas wells, the addition of surfactant was found effective in removing accumulated liquid and mitigating the occurrence of sectional slugged flow conditions. To investigate the drainage effect of water-based Sodium Dodecyl Sulfate (SDS) foam under the influence of inorganic salts, a further study was conducted with the presence of NaCl and MgCl₂ as environmental impact factors, and using metal grid sensors, a high-speed camera system, and pressure sensors. The findings revealed that the variation in foam properties resulting from the effect of inorganic salts had a substantial impact on the efficiency of foam drainage. Furthermore, it was observed that an excessive formation of stable foam within the pipeline caused a substantial increase in pressure drop along the route.

Conclusion When applying foam drainage technology to gathering and transmission pipelines with liquid accumulation, stability becomes a critical factor in selecting an appropriate foam system. Further research should focus on investigating the relationship between the influence of the foam layer on the flow characteristics of the medium in pipelines and the overall performance of the foam system.