Gas-lift wells can be unstable due to various reasons. The fluctuating, and sometimes chaotic unstable production behavior affects many offshore fields, particularly at their decline stages. The hazardousness of the flucuation to operation safety and smoothness has been awared. But the production reduction due to the instabilities has not been widely addressed. In this paper, a commercial available dynamical multiphase flow simulator is used to conduct investigation on the production loss. Two types of instabilities, casing heading and density wave instability, which both can result in production loss are simulated. Two hypothetic wells, abstracted from typical North Sea gas-lift wells, are built within the simulator. Parametric simulation study is then performed by changing the well settings. The average production rate of the unstable well can be obtained from the simulation and compared with the steady state prediction. The difference of the two results gives the production loss due to instability. Furthermore, the paper presents simulation results of applying feedback control to the unstable wells. The production loss is reduced as an effect of stabilization by feedback control.

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