The Use of Medium Molecular Weight Alcohol to Replace Electrolyte in EOR Formulation

Activity of most aqueous surfactant slugs for tertiary oil recovery is built up by electrolyte. This paper presents oil recovery data using an alternative method for making an active aqueous surfactant solution. Chemical slugs with high recovery activity and high viscosity are obtained by adding alcohols of C₆-C₁₂ to petroleum sulfonate solutions. The high viscosity developed in the slug renders the addition of polymer unnecessary and improves the displacement of oil significantly. Little emulsion is produced during the core experiments. Sandpack experiments performed under electrolyte-free conditions confirm that the activity of the solution comes from proper adjustment of the alcohol concentration. The concentration requirement can be explained by the formation of large surfactant aggregates in the active regions. The use of these medium molecular weight alcohols makes it possible to convert some petroleum sulfonates to active slugs when the addition of electrolyte is ineffective.