Liquid accumulation in deviated gas wells is a major challenge in production systems. Limitations with the use of gas lift, pumping or plunger lift methods add to this challenge. Recently, surfactants have been injected continuously or as batch to help with the well deliquification by foam generation. The batch treatment is done by intermittent application of soap sticks or liquid surfactants.
This study is an effort to characterize surfactant batch treatment as an artificial lift method in horizontal gas wells. Given the practical potential and yet limited number of studies on this topic, the results can provide an experimental source to optimize surfactant application in mature production systems.
The experimental study is performed in a 2-in ID facility consisting of a 64-ft lateral section with 1° downward inclination followed by a 41-ft vertical section. Water and compressed air are the liquid and gas phases, and an anionic surfactant is applied in batches at the heel of the well. First, static tests are conducted to analyze surfactant efficiency in well start-up conditions. The surfactant concentration, initial liquid loading level and gas rate are varied, and the final liquid loading volume is measured as the target parameter. Then, dynamic tests are conducted to mimic the flowing well conditions. Surfactant concentration, liquid and gas flow rates are varied, and pressure fluctuations at the toe are monitored with time. The surfactant batch is delivered after air-water flow stabilization to investigate the surfactant efficiency. In addition, a high speed camera is used to record the flow conditions.
For well startup conditions, surfactant batch treatment is most effective for lower gas flow rates. Furthermore, the efficacy of surfactants is more pronounced at lesser-loaded wells. The effect of increasing surfactant concentration is eminent below the critical micelle concentration (CMC) with no further improvement beyond CMC. Generally, surfactant batch treatment does not significantly improve well cleanup time.
During well production, surfactant batch treatment is most efficient in low liquid and gas flow rate systems. At increased liquid and gas flow rates, with increasing surfactant concentration, its use can be inefficient due to adverse effects caused by foam frictional pressure losses. When the surfactant batch treatment is efficient, its effect increases with increasing concentration until CMC is reached. During severe slugging, surfactant batch treatment eliminates the slug production phase and partially or fully eradicates the severe slugging depending on the severity of the slugs. Generally, no significant trends can be observed between the period of effectiveness and concentration of surfactant.