| When natural gas is produced from gas wells, it is always accompanied by liquid. At the later stages of a well's life, the gas is unable to carry liquid to the surface, resulting in liquid accumulation at the bottom of the well; this is called "Liquid Loading". Knowing when the liquid loading will occur is important because by using certain artificial lift methods the well can be produced under stable conditions even after the transition. The most popular method in the literature for determining the onset of liquid loading is the equation developed by Turner et al. This equation is a droplet model and is based on the terminal velocity of liquid droplet in single phase gas column. Many modifications have been proposed to this equation to improve the prediction of liquid loading. Recently, Veeken et al. have shown that in many inclined and some vertical wells, Turner's equation under-predicts the true critical flow rate (the flow rate at which liquid loading starts). This may be due to angle of deviation as well as the fact that inception of liquid loading is more likely due to liquid film reversal in annular flow rather than droplet fall back.;In this dissertation, the inception of liquid loading is defined using the liquid film reversal model based on experimental observation. Also, a new liquid loading model which is based on liquid film reversal is proposed. We base our model on Barnea's model and make several improvements to that model for better prediction of liquid loading. The improvements include: (i) development of variable film thickness model to account for the deviation angle of the well; (ii) development of equation to account for annular flow; and (iii) improvement of the friction factor equation at the interface between the liquid film and the gas core. We validated our model against all the available data from the literature as well as additional data collected from various operators. The results show remarkable improvement over Turner's original method as well as various ad hoc modifications made to that equation. A method which determines the unloading of a gas well after shut in will also be discussed.;In this dissertation, we also explore one possible method to eliminate liquid loading. Injection of surfactant is one of the common methods used for avoiding liquid loading in gas well. Using our definition of liquid loading, the stability of foam flow can be predicted. We also propose a correlation for liquid holdup in foam flow and compare the predictions with experimental data. Based on the large scale experimental data, we provide a preliminary model for predicting foam flow and articulate reasons why the foam works in preventing liquid loading. |
