Surfactant adsorption studied in digital core models

A paper appeared in Chemical Engineering Research and Design.

Scientists of the Institute of Geology and Petroleum Technologies have obtained new results in the field of physicochemical hydrodynamics, characterizing the influence of surface tension and boundary wetting angle on the adsorbed amount of surfactants.

Understanding the role and strength of factors affecting adsorption of surface-active agents (surfactants) during water flooding of oil-saturated porous media allows minimizing losses of expensive reagents and saving financial resources.

The goal was to investigate the effect of development parameters such as initial interfacial tension and wetting edge angle on the amount of surfactant adsorbed during oil displacement process. The novelty of the study lies in the investigation of mass transfer processes in digital cores under multiphase flow conditions.

“Sodium dodecyl sulfate, whose properties and adsorption isotherms are well studied, was tested as a surfactant. The most important results of the work include a map of the adsorbed amount of surfactant in the coordinates ‘interfacial tension – wetting edge angle. It is revealed that the increase of wetting angle, which characterizes the transition from the drainage flow to the impregnation mode, contributes to a significant increase in the adsorbed amount. It was found that the growth of initial interfacial tension contributes to the suppression of the adsorbed amount of surfactant”, commented Senior Research Associate Timur Zakirov.

The researchers studied a water-soluble surfactant, which has no ability to mix with the displaced oil. Under such conditions, the adsorbed quantity is determined by the contact surface area between the surfactant and adsorbent particles. In other words, mass transfer processes depend on the characteristics of multiphase immiscible displacement. The team showed that an increase in the wetting angle leads to an increase in the surface area of such contacts, while a decrease in interfacial tension, on the contrary, leads to its suppression.

“We are also working on the characterization of dynamic adsorption regimes depending on the flow rate and adsorption constant, which determines the intensity of mass transfer,” Zakirov noted.

It was found that at low mass transfer intensity, regardless of the interfacial tension and wetting angle, a decrease in the flow rate leads to an increase in the adsorbed amount. In contrast, when the adsorption constant is high, the amount adsorbed is determined by the displacement efficiency for a particular interfacial tension-wetting angle pair. For example, in the draining regime and at low interfacial tension, reducing the flow rate leads to suppression of the adsorbed amount of surfactant.

The obtained results are, first of all, of fundamental nature and are new in the field of physicochemical hydrodynamics, and can also serve as a basis for predicting the losses of valuable and expensive surfactants during field development.