Dynamic Interfacial Tension In Surfactant Enhanced Alkaline Flooding
Authors: Taylor Kevin C. , Hawkins Blaine F. , Islam M. Rafiq 
Published: March 2010

Dynamic interfacial tension behaviour has been identified in a surfactant-enhanced alkaline flooding process using David Lloydminster crude oil, sodium carbonate, and the surfactant Neodol 25–35. The magnitude of this dynamic behaviour was found to vary with the surfactant concentration.

Five linear corefloods in Berea sandstone were performed with different Neodol 25-3S concentrations. It was found that the initial interfacial tension value in each system, measured with the spinning drop apparatus, correlated with oil recovery efficiency. Further confirmation of this effect was found by comparison Son with literature values of oil recovery vs capillary number for linear Berea sandstone corefloods.

Introduction

In this paper, dynamic interfacial tension is shown to occur in surfactant-enhanced alkaline flooding. In such a process, the interfacial tension that occurs after initial oil/aqueous phase contact changes with time. The effect that this dynamic behaviour has on oil recovery in linear Berea sandstone cores is demonstrated. Dynamic interfacial tensions can occur when two immiscible liquid phases come into contact, provided one or both of the phases contains a surface-active material Interfacial tension between the two phases can change continuously with time until an equilibrium value is reached. During the course of attainment of equilibrium, the system may pass through an interfacial tension minimum. The possibility of this type of behaviour was mentioned by Wilson(1) and by Harkinsl21 in the 1920s. In 1952, the phenomenon was observed by Mansfield(3) with nujol/oleic acid in contact with a caustic solution, using the pendant-drop apparatus. England and Berg(4) described dynamic interfacial tension as the result of adsorptive accumulation of surface-active species at the interface, and observed the presence of adsorption and desorption barriers for the transfer of 1,5-pentanediol from white oil to water.

Dynamic interfacial tensions have been observed repeatedly for crude oil/caustic systems. The phenomenon of interfacial tension (IFT) reduction in this system was first reported by Atkin-son(5) and Nutting(6) in 1927. A more detailed investigation was carried out by Reisburg and Doschert(7), who looked at the effect of interface age and of sodium hydroxide concentration on interfacial tension. Jennings(6) examined 164 crude oils from 78 oil fields and measured IFT as a function of sodium hydroxide concentration using the pendant-drop method. He defined the term "caustic coefficient" as "the number of square cycles on log-log paper bounded by the caustic interfacial tension curve between interfacial tension values of 0.01 and 1.0 dyne/cm and caustic concentrations between 0.001 and 1.0wt%. A poor correlation between caustic coefficient and crude oil total acid number was found. However, 90% of the oils tested showed their lowest IFT with a sodium hydroxide concentration of 0.1 wt%, Jennings did not measure dynamic IFT behaviour.

McCaffrey(9) measured IFT between sodium hydroxide solutions and four crude oils using the spinning drop method(10). In some cases he found that IFT increased dramatically as the interface aged, which he attributed to the migration of soap products away from the interface after their initial formation.