An experimental study has been conducted in a co-current 127mm ID facility using air and silicone oil of 5cP viscosity. Results were obtained for passive lifting system, pump-assisted gas lifting and a fixed flow loop in the range of gas superficial velocities (Ugs =0.01 to 1.71m/s) and liquid superficial velocities of (Uls=0.01 to 2.00m/s). Void fraction data was obtained at five axial positions using two twin planes electrical capacitance tomography (ECT) sensors and a (32×32) wire mesh sensor (WMS). The WMS has been used to obtain information about void fraction and bubbles distribution. Three injector geometries have been employed, the effect of injection method on flow development, regime transitions, bubbles sizes and their distribution and the gas structures velocities has been investigated. The flow regimes observed in the test section ranges from dispersed bubbly flow to churn-bubbly regime.
Gas-lifting is achieved by injection of gas to the bottom of the wells to decrease the density of the fluids in the well's column, and accordingly decrease the gravitational pressure gradient without increasing much of the frictional losses. The gas-lift efficiency is dependent on many parameters that include, gas injection rate, type and geometry of the gas injector which affects the bubble size and concentration, and essentially the flow regime.
The mechanism by which gas is introduced near the base of the well has been reported to affect the efficiency of gas lift [1]. The injector geometry affects the initial bubble size distribution; introducing smaller bubbles should positively improve the lift efficiency as they have a lower rise velocity and therefore higher void fraction is achieved in the well for the same gas input. Hence, lower mixture density is generated in the well and therefore larger flow of liquid is produced. The effect of the gas injector on the bubbles' distribution extends to influence the lateral distribution of void fraction as smaller bubbles have more even distribution in the cross-section resulting in a higher void fraction and therefore better efficiency. Moreover the injection method have a great influence on the bubble relative velocity, bubbles coalescence and break-up, time/space variation of void fraction and the flow pattern transition which affects the system stability [2]. The majority of the previous investigations on gas lift have been carried out on relatively smaller pipes and for considerably less viscous fluids. This paper will be reporting the experimental campaign conducted in a 127mm (5 inches) internal diameter using 4.83cP silicone oil.
