Influence of surfactant and electrolyte concentrations on surfactant adsorption and foaming characteristics

Abstract

Surfactant adsorption and foaming characteristics are influenced by surfactant concentration and presence of inorganic electrolytes. Hence, it should be possible to optimize the performance of the surfactants in subsurface applications by understanding the influence of these parameters on surfactants. This study investigates the adsorption of sodium dodecyl sulfate (SDS) on kaolinite as a function of surfactant concentration and added electrolyte (NaCl, CaCl2and AlCl3) concentration. Influence of temperature on the electrolyte and surfactant interactions was also examined. Adsorption isotherms were obtained using surfactant concentrations higher and lower than the critical micelle concentration (CMC). Surfactants adsorption on kaolinite was determined using a surface tension technique and two phase titration methods. Adsorption data were analyzed by fitting with Langmuir and Freundlich adsorption isotherms. The foam was generated by dispersing CO2gas into the surfactant solution through a porous stone. Foam half-life and the rate of foam collapse as function of time was monitored. The adsorption of SDS by kaolinite increases with the increasing concentration of NaCl and CaCl2and decreasing temperature. However, adsorption in presence of AlCl3shows different behavior. The adsorption remains constant irrespective of the increasing AlCl3concentration. Results show that the adsorption of SDS onto kaolinite in presence and absence of salts follows the Langmuir isotherm models. Salts containing trivalent ions and divalent ions (AlCl3and CaCl2) were found to increase SDS adsorption on kaolinite and decrease bubbles stability compared to salts containing mono ions (NaCl). The order of increase in surfactant adsorption and bubble coalescence in presence of salts is as follows: AlCl3>CaCl2>NaCl. There was an optimum surfactant concentration corresponding to maximum foam stability beyond which there was either a reduction or no significant changes in foam stability. This concentration decreases in presence of salts, except for AlCl3and high concentrations of NaCl (5�wt%) and CaCl2(1�wt%). The presence of salt improved foam generation and bubble stability at SDS concentration below the CMC. Above CMC, the bubble coalescence inhibition and foam stability decreased in the presence of salt. Decrease in surfactant surface tension and CMC, the screening effect of electrostatic double layer (EDL) by salts and the ability of SDS to form a complex with divalent (Ca2+) and trivalent (Al3+) cations are critical factors affecting SDS adsorption and foaming behaviors in presence of AlCl3,CaCl2and NaCl salts. The results of this study have wide applications in the design, implementation and optimization of chemical EOR in the field.