A Correlation Of Interfacial Charge With Various Interfacial Properties In Relation To Oil Recovery Efficiency During Waterflooding
Authors: Chiang M.Y. , Chan K.S. , Shah D.O. 
Published: March 2010

Abstract
The objective of this study was to correlate the interfacial charge with other properties of the crude oil/brine interface in relation to oil recovery efficiency. The dispersed droplets of Seeligson crude oil in brine solution exhibited a maximum in electrophonetic mobility at 3.5% NaCI concentration. At the same NaCI concentration, the drop volume of the crude oil in brine was minimum, which suggested that the interfacial tension was also minimum. Moreover, minimum interfacial viscosity between a thin crude oil film and brine occurred at 3.5% NaCI concentration. The surface-active components in the crude oil were eluted by chromatography in silica gel columns. The results showed that a maximum amount of surface-active material was eluted by 3.5% NaCI. We propose that the striking changes observed at 3.5% NaCI concentration are due to the maximum surface charge density at the crude oil/brine interface.
Furthermore, we observed the maximum oil recovery efficiency in sandpacks and Berea cores when the crude oil-was displaced by 3.5% NaCI brine. Because contact angle measurements of crude oil droplets on quartz plates submerged in brine did not show a significant change at 3.5% NaCI the wettability alteration as a possible mechanism for enhanced oil recovery in this system is ruled out. The capillary number at 3.5% NaCI also remained below 10−6 and hence cannot account for the enhanced oil recovery. A possible explanation for the maximum oil recovery efficiency at a specific brine concentration is proposed in terms of interfacial charge at the crude oil/ brine interface and that at the sand/brine interface. It is further emphasized that surface charge is an important parameter which can influence interfacial tension and interfacial viscosity at the oil/brine interface.

Introduction
Since the first field application in 1865(1), the water- flooding process for oil recovery has evolved from plain water injection to the complicated processes involving the addition of solvents, chemicals, gas or heat. These additives change either one or several of factors such as water mobility (2,3), oil viscosity(4,5), rock wettability (6,7) and wateroil interfacial tension(8,9,10). The incorporation of these additives increases the oil displacement efficiency, the sweep efficiency, or both. Therefore, it is evident that in order to achieve a better oil recovery the physical and chemical properties of the injected brine are of the utmost importance. The main objective of this investigation was to elucidate the influence of salt concentration on the properties of the crude oil/brine interface and to correlate it with the oil displacement efficiency in sand packs and Berea cores.

Experimental Materials and Methods

Materials
The crude oil used in all experiments was obtained from Seeligson Oil Field, Texas. It was collected at the wellhead prior to the addition of any agents and shipped directly to us from the field. The crude oil had 39.4 °API and a viscosity of 2.54 cp at 25 °C.
The brine solutions were prepared by adding NaCI to deionized-distilled water on the weight per cent basis.