Abstract
An experimental study of severe slugging suppression utilizing a combination of surfactants and gas-lift was conducted using a facility consisting of a 3-in. ID, 65 ft long, -3° inclined flow line followed by a 45 ft long vertical riser system. Air and water were used as fluids. The surfactant used was a foaming agent capable of forming stable foams in all brines for a wide range of pH. Pressure behavior in the flow line – riser system was monitored and input gas, injection gas, liquid and surfactant flow rates were continuously measured. In addition, visual observations were made to identify severe slugging. Effects of the proposed method were quantified with a modified elimination performance index (MEPI) considering not only pressure fluctuations but also back-pressure effects.
A total of 30 tests were conducted. The data were analyzed for the severe slugging suppression of the surfactant and gas-lift combination, the effect of gas lift on surfactant injection, and the effect of the surfactant on the reduction of the gas-lift gas. The combination technique with the highest gas-lift rate completely eliminated the severe slugging for the all of the tests conducted. Surfactants were able to suppress severe slugging for most of the cases. The performance of "Only Surfactant Injection Case" increases as the gas-liquid ratio increases. For all of the tests, back-pressure reduction was observed. MEPI is used as the main parameter to assess the performance of the severe slugging suppression methods. Gas-lift not only contributes with density reduction through volumetric increase of gas in the riser but it also reduces the mixture density by promoting more foam generation. There were reductions in the gas-lift rate from the original maximum gas-lift injection rate for all the tests conducted with surfactant injection.
