Quantitative analysis of an amphoteric surfactant in acidizing fluids and coreflood effluent

Viscoelastic surfactants (VES) exhibit remarkable viscoelastic character due to their ability of forming wormlike micelles and entangled structures, which can greatly increase the viscosity of the fluid. The VES fluids can be used to improve the proppant suspension ability and fluid diverting ability in well acidizing treatments. As a result, VES have been found numerous application in the oil fields as fracturing fluids and matrix acidizing fluids in the recent years. According to previous studies, the concentration of VES in the fluids has profound effects on their performance downhole. Additionally, the loss of VES is also a very important indicator of the downhole events. Therefore, being able to analyze the concentration of VES surfactants in both live and spent acids is of great importance for production engineers who apply VES in the oil fields. In the present work, a two-phase titration method was optimized for the quantitative analysis of a carboxybetaine viscoelastic surfactant, and the interference by typical additives in the acidizing fluids on this method was determined. This method was used in the determination of coreflood effluent, and it was found that tremendous amount of the viscoelastic surfactant is trapped in the core.