As the flow rate in gas wells decreases, the liquid content of the well increases (wellbore load up). This can eventually cause the well to die. For many years, people have used the Turner correlation to predict the minimum rate the well can produce without loading. The Turner correlation is based on the gas velocity being too low to lift droplets from the well. Several investigators have found that the droplet entrainment mechanism is wrong, and that the actual mechanism for wellbore load up is the reversal of the liquid film on the walls of the pipe. The film reversal point corresponds to the transition between annular flow and wavy annular/churn flow. Using this criterion as the basis, the film reversal point was well correlated by use of a modified Froude number, which was shown to give good results for pipes between 4 and 200 mm (1.5 and 8 in). Using this approach, a film reversal point was found for angles from near-horizontal to vertical. The model was compared with published wellbore load-up data and was found to give as good or better predictions than the Turner model. The new model also properly accounts for pipe inclination, diameter, and surface tension effects.

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