Effects of flow rate and alkali-to-acid ratio on the displacement of acidic oil by alkaline solutions in radial porous media

Alkaline flooding is a method of enhanced oil recovery that relies on the formation of surface-active substances in situ by a chemical reaction between acidic components in the oil and an alkaline reagent. As the injected alkali advances through the porous medium, it keeps contacting fresh oil. At some moment dependent on the alkali/acid concentrations and the velocity, the alkali at the advancing front may become depleted and the flood becomes interfacially nonreactive. The present study is aimed at investigating the above-mentioned phenomena. Displacement studies were conducted in radial cells containing sintered glass beads as a porous medium. Light paraffin oil acidified with 10 mmol/L of linoleic acid served as the displaced (oil) phase while the displacing aqueous solution contained 0-25 mmol/L of sodium hydroxide, The highest oil recovery was obtained under the conditions of low flow rate and high alkali concentration. Increasing the flow rate at high NaOH concentration resulted in decreasing oil recovery up to a certain threshold flow rate. Conversely, the amount of oil recovered by waterflooding only (no alkali) initially increased with increasing how rate up to the same threshold flow rate beyond which there was no difference between the alkaline flood and a waterflood. (C) 2000 Academic Press.