The Evaluation Of Surfactant Systems For Oil Recovery Using Statistical Design Principles And Analysis
Authors: Gerbacia W. 
Published: December 2007

Gerbacia, W., Chevron Oil Field Research Company

Abstract
A statistical response surface design procedure was used to investigate the procedure was used to investigate the effect of petroleum sulfonate concentration, alcohol chain length, and the alcohol-sulfonate ratio on salt tolerance, conductivity, viscosity, interfacial tension, and oil recovery properties of aqueous surfactant solutions. This procedure greatly reduced the number of procedure greatly reduced the number of data points which were required to develop significant correlations.
Regression analysis of the data showed that calcium tolerance was chiefly dependent on sulfonate concentration, and to a smaller extent, on the alcohol chain length. A correlation was found between specific conductance and alcohol chain length, and specific conductance and sulfonate concentration. Viscosity was found to increase with the hydrocarbon chain length of the alcohol and the ratio of alcohol to sulfonate. The interfacial tension was dependent only on the sulfonate concentration within the limits of the variables studied. None of the surfactants produced very low interfacial tensions (less than 10 to the -2 dyne/cm) with the crude oil used in the investigation, nor were high displacement efficiencies observed.

Introduction
There are a number of factors which can influence the efficiency of a micellar crude oil recovery process. The micellar fluid is usually composed of a number of components, such as surfactant, cosurfactant, solvent, salts, etc. and varying these compositional parameters can affect the properties which influence the crude oil properties which influence the crude oil displacement efficiency of the chemical system.
Several studies have been reported in the literature (e.g. ref. 1–3), which demonstrate the general trends of different properties of surfactant solutions under properties of surfactant solutions under various conditions. Such information is very helpful, but it is still necessary to determine the specific character of the micellar solution for a given crude oil/brine system. It is also important to consider interactions among the independent parameters which may be concealed by experiments in which only one parameter is changed at a time. For instance the effect of an alcohol used as a cosurfactant may be a function of surfactant concentration.
In this work a broad approach was taken in studying the effects of three selected independent variables on a number of properties of surfactant dispersions. properties of surfactant dispersions. The independent variables were linear alcohol (cosurfactant) chain length, alcohol-sulfonate ratio, and sulfonate concentration. Six responses to these variables were measured: sodium chloride tolerance, calcium chloride tolerance, conductivity, viscosity, interfacial tension, and crude oil recovery. A rotatable response surface experimental design developed by Box and Behnken was used to choose the combinations of independent variables. This design allows one to estimate variable effects with a smaller number of experiments than would be required for a full factorial design. For example, a full factorial design for the three levels of the independent variables used in this study would require 27 data points. The Box-Behnken design requires 15.