Modeling of Liquid Unloading in Vertical Gas Wells in the Presence of Foam

Abstract

Summary Liquid loading is one of the production challenges in gas wells, leading to accumulation of produced liquid and thereby reduction of gas rate. One of the proposed methods of liquid unloading is to generate foam at the bottom of gas wells. In this paper, we provided a modified film model, so-called foam- assisted film model (FAFM), to describe the performance of foam for liquid unloading in vertical gas wells. In this model, there is possibility for loaded liquid to be partially present in the center of tubing along with gas phase in the form of slug flow regime. This condition potentially provides foam generation in the center of tubing in addition to foam film generation over the tubing wall, when an appropriate foaming agent is present at the bottomhole. Model results showed that as surface tension between gas and liquid phase decreases, foam performance during liquid unloading increases. According to gas well conditions used in this study, as well tubing diameter decreases from 4 to 2 in, required foam flow rate for liquid unloading decreases as much as four-time. Results of this study showed potential application of FAFM model to predict critical gas rate for a successful gas well deliquification.