Characterized as the reversal flow of liquid film into the wellbore, liquid loading is a genuine issue for gas wells as it diminishes the gas production rate. In the event that fluid rate accumulating in the wellbore is excessively high, the gas production rate will decrease fundamentally and for severe instances of accumulation, the operating organization will relinquish the well which will cause immense budgetary misfortunes. Subsequently, so as to maintain a strategic distance from the latter occurring, it is proper for the working organization to anticipate and recognize the liquid loading status of the gas wells in order to utilize viable apparatuses and pathways to avert it. Therefore, to counteract those misfortunes, the forecast of the liquid reversal point is obligatory.
Several researchers studied and established models to predict the loading phenomenon. After thoroughly review those studies, conclusions made on the different models are controversy and their results are conservatives. This paper presents a model where the hypothesis relies on fluid film reversal. The model considers the change from annular flow (fluid film encompassing the gas core) to slug or churn flow to be the grounds of liquid film backflow. Subsequently, from the review of previous literature on vertical wells, it is obvious that the film thickness is more sensitive to the tubing inner diameter, the tubing pressure gradient, the changes of fluid properties, the film and gas gravitational forces. Therefore, it is more rational for the critical gas flow rate to be dependent on those parameters. Subsequently, the momentum balances of both the liquid and gas phase were developed, and a derivation of an expression of the gas void fraction leading to the derivation of the dimensionless liquid film thickness and thus the critical film thickness were obtained. As a result of this modeling, a simplistic practical critical gas velocity and critical gas flow rate correlation which at the same time combines and incorporates the parameters influencing the loading phenomenon are viable for any profundity of the well.
So as to assess the adequacy of this model, evaluation has been performed between the model and some well-known model such as Turner et al. (1969) model, Li et al. (2001) model, Belfroid et al. (2008) model and Liu et al. (2018) model on some of the vertical gas wells of the North-West Xinjiang gas field. The outcome of this evaluation provides an overall 95% prediction and identification precision, outclassing the models quoted above. Thus, the model is the most appropriate to classify and foresee liquid backflow and accumulation in gas wells.
