Impact of surface choking on gas-lift stability and flow behaviour in oil producing wells

The effect of surface choking on gaslift stability and flow regime transition in vertical cylindrical pipe during gaslift operation is investigated. Here, a laboratory scale multiphase flow rig was designed, fabricated, and assembled. Gas rates of 0.000113 m3/s and 0.000187 m3/s were imposed on a 1 mm single nozzle injector. Surface choking was implemented by setting the system to 15%, 25%, 50% and 100% opening. For each opening condition, transient pressure at four locations; corresponding to length-to-diameter ratios of 0.0, 18.3, 36.7, and 53.3, was recorded. Flow structure and regime transition are characterised by visual, photographic and slow-motion videos, recorded at each location. A transition from random peak-to-peak cyclic and periodic pressure oscillation, accompanied by pressure increase, is observed. Further, bubble size reduction characterised by low vorticity and turbulence is observed at 15% opening. It is concluded that surface choking must be complemented by knowledge of flow behaviour within the system.