Liquid loading is the mechanism that is associated with increased liquid hold-up and liquid back-flow at lower gas flow rates in gas production wells. In the laboratory, most liquid loading experiments are performed at fixed gas and liquid rates (mass flow controlled). In the field, the well behaviour is a coupled well-reservoir system in which the reservoir results in a pressure or mass flow controlled inflow, depending on the reservoir characteristics. In this paper, results are presented for experiments which have been performed with a pressure controlled vessel attached to a vertical pipe. The pressure drop was varied to represent reservoir characteristics from tight to prolific. Liquid was injected using a mass flow controller.

From these experiments, it was concluded that the flowrate at which loading occurs can be predicted by the overall pressure drop curve. That is the pressure drop from vessel to separator and not the tubing pressure drop curve. A numerical investigation confirms this for pressure dependent liquid injection. This stability point can be at a higher or lower velocity than the actual loading/flooding point. The results of these experiments are elaborated briefly. The main focus of this paper is the evaluation of the influence of external disturbances on stable flow conditions. A stable system is defined as a system in which the conditions are such that gas flow is possible and will not stop. At unstable conditions, the gas flow starts to drop. In the experiments described in this paper, it was found that the required external disturbance to destabilize a system is related to the pressure drawdown.

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