A Comparative Evaluation of Microemulsions and Aqueous Surfactant Systems
Authors: Bae J.H. , Petrick C.B. , Ehrlich R. 
Published: December 2007

This paper was prepared for the Improved Oil Recovery Symposium of the Society of Petroleum Engineers of AIME, to be held in Tulsa, Okla., April 22–24, 1974. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon requested to the Editor of the appropriate journal, provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussions may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Abstract
An oil-external microemulsion, a water-external microemulsion, and an aqueous surfactant solution were prepared using identical concentrations of petroleum prepared using identical concentrations of petroleum sulfonates and cosurfactant for the purpose of making a comparison of these systems for secondary or tertiary recovery. The criteria used were: oil-water interfacial tension, adsorption on reservoir rock, and stability with divalent ions and high salinity brines.
It was found that the oil-external micro-emulsion showed both higher adsorption and higher oil-water interfacial tension than the other systems. However, the oil-external system showed a better tolerance for brine and divalent ions. It is concluded that the aqueous solution would be the best choice among the systems tested with the present formulation.

Introduction
Surfactant flooding is a process in which a surfactant or a combination of surfactants and cosurfactants is introduced into a reservoir to increase oil recovery. By lowering the interfacial tension between oil and water, discontinuous residual oil globules trapped in the pores of the rock by capillary forces can be made to flow. With the shortage of crude oil supply and the availability of petroleum sulfonates that give extremely low interfacial tension, this process lately attracted much attention as a secondary or tertiary recovery method.
A surfactant system must have the ability to lower the oil-water interfacial tension in order to mobilize the residual oil. It should also propagate through most of the reservoir without losing this ability. Unfortunately, the surfactant slug usually breaks down under reservoir conditions. This breakdown can be caused by excessive adsorption of surfactants on the rock surfaces, precipitation of surfactants by reservoir brine of high salinity and divalent ion content, or penetration of the slug by drive water due to adverse mobility. Thus, the main technical problem areas in surfactant flooding are:the attainment of low oil-water interfacial tension,surfactant adsorption,brine compatibility and temperature stability, andmobility control.
Presently, the surfactant flooding process may be classified according to the mode of transportation of surfactants into the reservoir: the microemulsions and aqueous surfactant solutions. When surfactants are transported in the form of microemulsions, it can be either oil-external or water-external.