The analysis and design of gas lift strings in oil wells have been done without considering the transient effect of multiphase flow in pipes. The reason for this fact relies on the complexities aspects of unloading gas lift wells since the initial static condition(dead well) until the condition of stabilized flow. At the begining, the annulus space may contain liquid at any level which is pushed downward in a piston like manner by the injected gas. The reservoir is represented by the inflow performance curve (IPR). The problem is solved by a computer model based on the liquid and gas mass conservation laws and the momentum conservation law of the mixture. The model couples the annulus and the upward vertical multiphase flow through gas lift valves. Mass transfer between phases is not considered. Operational variables (pressure, superficial liquid and gas velocities, slippage liquid hold up) are displayed as functions of time and depth. Gas injection rate at surface, liquid and gas flow rates through gas lift valves, as well as pressure profiles in the annulus space are also monitored with time. Proposals for new transient analysis and design of gas lift installations are suggested.

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