Foam stability: The key to inhibiting slug generation in gas–liquid flow

Abstract

Surfactant-based foam drainage technology is a favored method of liquid accumulation removal, and it has been demonstrated as an efficient way to improve gas production efficiency. However, foam properties are extremely complex and the same surfactant can produce foam systems with widely varying properties under different environmental conditions. This has a huge impact on the multiphase flow containing foam and thus on the efficiency of fluid removal. To further explore the influences of changing foam properties on the flow characteristics and the liquid-carrying capacity of foam, this study experimentally investigated the gas–liquid multiphase flow containing different foams in a hilly terrain pipeline with different properties in pipelines by adding SDS surfactant and MgCl2. The results show that the foam stability can significantly affect the gas–liquid multiphase flow characteristics. Adding MgCl2 enhances the stability of SDS foam. This narrows the range of intermittent flow conditions and leads to a significant fall in the critical gas velocity corresponding to the transition from intermittent to separated flow. Meanwhile, under the same gas and liquid velocities conditions, the foam with higher stability has a more pronounced suppression effect on the velocity of liquid in the upward inclined section, both the slug velocity and the liquid reflux velocity. The reduction in the holding rate also indicates that a more-stable foam improves the liquid-carrying capacity of gas and the discharge efficiency. In addition, as the gas velocity increases, the enhanced stability promotes the transition of the flow pattern from stratified to annular flow, resulting in a remarkable increase in the pressure drop gradient. This suggests that a more stable foam system is suitable for environments with lower gas velocities.