This　study　presents　surfactant　injection　as　a　replacement　technology　for　mechanical　pigging　to　reduce　liquid　accumulation　for　wet　gas　transmission.　The　hilly　terrain　gas/liquid　flow　development　characteristics　under　surfactant　injection　were　explored　in　pipelines,　and　a　comprehensive　experiment　was　performed　through　flow　observation　and　the　measurement　and　analysis　of　the　flow　characteristic　parameters.　The　250　ppm　sodium　dodecyl　sulfate　(SDS)　surfactant　was　employed　according　to　the　variation　characteristics　of　the　flow　pattern　and　pressure　drop　at　different　concentrations.　Flow　observations　and　liquid　holdup　characteristics　indicate　that　owing　to　the　formation　of　aqueous　foam,　the　gas/liquid　interface　and　phase　characteristics　change　significantly,　and　the　liquid　holdup　decreases　by　several　or　even　more　than　ten　times　and　maintains　a　low　value　(0.004–0.070),　except　for　the　initial　gas–liquid　flow　at　low　gas　flow　and　high　liquid　flow　rates.　The　aqueous　foam　effectively　suppresses　the　slug　and　pseudo　slug　initiation,　the　gas/liquid　convection　of　the　slug　body,　and　the　large　wave　rolling　of　the　pseudo-slug　body,　which　induces　the　dissipation　of　intermittent　flow.　The　pressure　drop　under　the　influence　of　aqueous　foam　decreases　drastically　(60%　∼　85%)　at　certain　gas　and　liquid　velocities　and　fluctuates　smoothly　near　zero　over　a　wide　experimental　range.　The　surfactant　suppression　on　partially　blocked　pseudo-slug　body　induces　a　significant　decrease　of　pseudo-slug　frequency　from　0.17　∼　0.42　Hz　to　0　∼　0.06　Hz　and　transitional　velocity　from　1.21　∼　1.90　m/s　to　0　∼　1.11　m/s.　This　research　is　highly　significant　for　surfactant　injection　schemes　and　efficient　and　sustainable　production.　©　2023　Elsevier　Ltd