System Analysis of Liquid-Assisted Gas-Lift Unloading

Abstract

Abstract This study describes the concept of Liquid-Assisted Gas-Lift (LAGL). This concept includes three main parts: two-phase downward flow in annulus, two-phase flow through orifice Gas-Lift Valves (GLVs), and upward two-phase flow in pipes. The latter part is well described in the literature and will not be investigated in this work. However, there is a lack of studies on two-phase downward flow in annulus and through GLVs. Therefore, these two topics are investigated in this work. An experimental and numerical study on two-phase flow through orifice GLVs is presented. The experimental results are compared to predictions using a numerical model published in the literature for two-phase flow through restrictions. It is observed that the mechanistic model could successfully characterize two-phase flow thorough gas-lift valves with errors lower than 10%. A flow regime map of downward two-phase flow in the annulus is used to analyze the flow regimes observed during field-scale experiments of LAGL unloading. It was concluded that the intermittent and bubbly flow are preferred to minimize injection pressure during LAGL unloading operations. A commercial flow simulator is used to perform sensitivity analysis of the LAGL system and to perform unloading of a well using the LAGL concept. The unloading simulation results indicated that the use of LAGL has the potential to decrease the injection pressure requirement in more than 50% when compared to the conventional single-point gas injection. The simulation model is shown to be a useful tool to perform system analysis and optimization of LAGL.