Feasibility of using polymers to improve foam flow performance in vertical pipes: Application to liquid unloading in gas wells

Abstract

Foam unloading is a cost-effective technique for removing liquid from low-energy gas wells, but it faces challenges due to thefoam stability at the wellbore. Surfactants alone struggle to create and maintain durable foam films under wellbore conditions. Polymers are known to enhance foam stability by increasing lamella thickness and viscosity, however their impact on foam unloading has not been well explored. This study investigates the effects of Xanthan Gum (XG) and Polyvinylpyrrolidone (PVP) polymers on stability and unloading efficiency of the foams made by Alkyl Polyglycoside surfactant. The research evaluates foam stability and examines the bubble size and lamella thickness under varying salinity conditions. Additionally, the study estimates foam unloading efficiency by determining unloaded mass rate, critical gas velocity and Weber number. Results show that polymer concentration, type and molecular weight significantly affect foam morphology and stability. Xanthan Gum at 1000 ppm demonstrated the smallest bubble size and greatest foam stability. This concentration also achieved the highest unloaded mass, 30 % more than the surfactant-only case. Regarding the molecular weight of the polymers, HPVP demonstrated an ability to generate smaller bubbles in comparison with LPVP. Consequently, HPVP exhibited superior performance in liquid unloading, surpassing LPVP by a margin of 8.5 %. The addition of polymers reduced critical gas velocity, with 1000 ppm of XG yielding the lowest value. Initially, the Weber numbers for polymer-stabilised foams were higher than the surfactant-only case (XG: 208.01, LPVP: 17.70, HPVP: 26.38 vs. APG: 2.25) due to the Marangoni effect but decreased during the unloading process (XG: 788.58, LPVP: 1850.26, HPVP: 1702.01 vs. base case: 4046.42), indicating improved stability and performance. Overall, the study demonstrates that polymers can significantly improve foam stability and performance, maintaining foam integrity throughout the unloading process if engineered properly prior to their application.