Producing gas wells faces with the challenge of liquid loading mostly in later stages of production. Due to formation of liquid coloumn in the wellbore, the rate decreases below the critical rate. Hence, water reduces well performance. Depending on the wells, liquid coloumn can form because of either entrance of formation water to the wellbore in dry gas wells or wet gas liquidification in wet gas wells or condensation in gas-condensate wells. In all the cases, as a result, bottomhole pressure increases and reservoir pressure does not have enough pressure to force the liquid to the surface. This leads to considerable reduction of well production and that may lead into seizure flow in more severe cases. In last decades, different techniques and correlations have been offered by many authors for determination of critical liquid loading rate. This paper reviews the existing several widely used liquid loading models and highlights their advantages and drawbacks. Additionally, at the end of the paper, a case study has been conducted for these models to identify their applicability conditions and limitations regarding the selection of best matched based on well data. According to the case study's results, Guo's model predicts critical flow rate more accurately than all other models. There's no any applicability ranges, which it can be applied to all vertical gas wells with different wellhead pressures. When it comes to the other models, their applicability ranges should be taken into account carefully for not to ending with incorrect estimations.

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