Optimization of Intermittent Defoamer Injection in Foam-Assisted Gas-Well Deliquification: Experimental and Theoretical Investigation

Low-pressure gas wells treated by foam-assisted deliquification often suffer from poor temporal coordination between foamer and defoamer injection, excessive defoamer consumption under continuous dosing, and foam carryover into surface facilities. This study proposes a coordinated intermittent strategy based on the complete foam-transport timeline. A visual vertical-pipe facility quantified the effects of chemical concentration on foam generation, liquid holdup, frictional pressure loss, and foam collapse. A gravity-driven annular falling-film model predicted the time required for the foamer to reach the bottomhole. The wellbore was then discretized, and local liquid holdup was coupled with actual liquid velocity to predict foam return from the bottomhole to the wellhead. Together, the models determine the defoamer start time, injection duration, and dose. Increasing foamer concentration reduced liquid holdup but increased flow resistance above an effective range; excess defoamer likewise produced little additional collapse. In a tight-gas well, the optimized schedule maintained liquid unloading and stable surface operation while reducing daily defoamer consumption from 36 to 6 L and chemical cost by more than 80%. The method provides a quantitative basis for digitally controlled chemical dosing in foam-assisted gas-well deliquification.