Impact of Acid Additives on the Rheological Properties of Viscoelastic Surfactants and Their Influence on Field Application

Abstract

Abstract This paper examines a new class of viscoelastic surfactants (amphoteric) that are used to enhance sweep efficiency during acid injection. Surfactant molecules align themselves and form rod-shape micelles once the acid is spent. These micelles cause the viscosity to significantly increase, and induce viscoelastic properties to the spent acid. The enhancement in these properties depends on the micelle shape and magnitude of entanglement. The effects of acid additives and contaminants (mainly iron (III)), on the rheological properties of these systems were examined over a wide range of parameters. Viscosity measurements were conducted on specially designed viscometers to handle very corrosive fluids. Measurements were made between 25 and 100°C, and 600 psi at various shear rates from 58 to 1,740 s−1. Acid additives included corrosion inhibitors, inhibitor aids, iron control agents, hydrogen sulfide scavengers, anti-sludge agents, and nonionic surfactants. Effects of mutual solvents and methanol on the apparent viscosity were also investigated. It is observed that temperature, pH, shear conditions and acid additives have a profound influence on the apparent viscosity of the surfactant-acid system. The viscosity and related properties are very different from what we have observed with both natural and synthetic polymers. These properties were characterized and correlated with the type and nature of the additive used. Optimum conditions for better fluid performance in the field were derived.