Abstract: Foam drainage and gas recovery technology is widely used in various gas fields, especially low permeability gas reservoirs at home and abroad due to its low cost, simple construction and quick results. It plays a leading role in many drainage and gas recovery processes. It is of great significance to accurately reveal the flow pattern and the liquid carrying rule of the bubble discharge well in order to optimize the technological parameters of bubble discharge process and improve the technological level of foam drainage and gas production. Therefore, in this paper, a set of 30 mm diameter visual experimental equipment was set up to carry out the experimental research of surfactant effect on the flow characteristics of gas-liquid twophase flow under different surfactant concentration, inclination angle and gas-liquid ratio. By comparing the flow characteristics with and without surfactant, surfactant effect on flow pattern, structure and transition boundary of gas-liquid two phase flow in vertical pipe were analyzed. The experimental results show that: 1) The addition of surfactant promotes the slug-to-churn and churn-to-annular transition were shifted to somewhat lower gasflow rates. Simultaneously the foam was better able to suppress the intermittent flow, leading to a narrower range of slug flow and churn flow. 2) The pressure gradients of surfactant solutions were lower than those of pure water especially in slugflow and churnflow regimes, with less irregular flow at low gas velocity. However, the pressure difference of annular flow increased rapidly along the increase of concentration. 3) The liquid holdup was much smaller with surfactant, while tended towards stability by the change of concentration at higher gas flow rate. 4) After surfactant addition, the critical gas velocity decreased sharply by over 40% at inclination angle about 50 ° especially.

Key words: gas well, liquid remove from gas well, surfactant, foam-gas-liquid flow multiphase, flow regime, pressure drop, liquid carrying