An Acoustic-Based Method for Measuring Surfactant Concentration in Field Applications

Abstract

Numerous enhanced oil recovery (EOR) techniques entail injecting chemical treatments such as surfactants at a predetermined concentration to achieve targeted results. Typically, these formulations are prepared on-site prior to injection into the reservoir using large mixing tanks. The current quality assurance practice for proper concentration of treatment materials uses indirect methods such as interfacial tension (IFT) and/or viscosity measurements. These measurements can be lengthy or only suitable for a specific range of dispersed phase volumes. We examined the prospect of using acoustic measurements as a method to determine surfactant concentration for quality assessment of chemical injections on-site. The advantage of ultrasound is that it can characterize both concentrated systems and low dispersed phase volumes. In this study, we acquired the sound attenuation of an amphoteric surfactant, Cocamidopropyl Hydroxysultaine (CBS), and in-house petroleum sulfonate surfactant nano-capsules (NanoSurfactant), within a frequency range of 3-99.5 MHz. We conducted a set of experiments to establish the relationship between acoustic attenuation and surfactant concentration, and assess the measurements’ dependence on variable factors including applied frequency, suspending fluid, and temperature. The data showed a nearly perfect linear fit in the higher frequency range (65-99.5 MHz) where the coefficient of determination was between 0.979-0.998. Consistent with theoretical predictions, this method showed sensitivity to water salinity where the surfactant, at a constant concentration, displayed higher attenuation values in response to the increase in water salinity, allowing the contribution of surfactants to the acoustic attenuation to be isolated. Our method accurately determined surfactant concentrations using acoustic attenuation regardless of the surfactant used. Adopting such a robust protocol that can determine surfactant concentration and has the potential to improve field quality assurance methods would be beneficial for EOR research and industry applications whether as a standalone system or in conjunction with other commonly available methods.