Current status of CFD modeling of liquid loading phenomena in gas wells: a literature review

Two-phase (gas–liquid) flow in vertical pipes has been one of the interests of industrial applications such as power plants, nuclear reactors, boilers, gas well exploration and so on. One of the problems usually encountered in the gas well exploration industries is liquid loading: a condition where the gas velocity is not high enough to carry all the liquid generated in the gas wells. During normal operation, flow in the gas wells shows characteristics of annular flow regime. However, as the gas wells mature, the gas velocities reduce (below a critical value) and gradually lead to the onset of liquid loading (film reversal). At this point, flow in the gas well presents features of churn flow. Thus, during the film reversal point, the liquid film tends to increase in thickness and part of it starts to flow downwards. This paper first summarizes the available mechanistic and numerical models related to liquid loading and then reviews the application of CFD techniques to liquid loading modeling in vertical pipes. Most of the methodologies discussed here focus on annular and churn flow due to the limited information on the application of CFD techniques to liquid loading modeling and the onset of film reversal occurs during the transition from annular flow to churn flow which can lead to liquid loading as observed experimentally by many researchers. It was concluded from the available literature related to liquid loading that a detailed understanding of the fluid flow behavior during liquid loading is not yet fully available and prediction methods of this phenomenon are still rather incipient. Directions for good CFD modeling of these important phenomena are presented in the present paper.