Wetting Properties of Chalk – Impact of Water Soluble Acidic Material in Crude Oil

Carboxylic material present in the crude oil, quantified as acid number (AN), is believed to be the most<br>important wetting parameter for carbonates. The water wetness decreases as the AN increases. At high<br>temperature, seawater is able to displace some of the adsorbed carboxylic materials, and seawater<br>therefore acts as a wettability modifier causing increased oil recovery both by spontaneous imbibition and<br>by forced displacement. It has been documented that interactions between ions present in seawater, Ca2+,<br>Mg2+ and SO42-, and the chalk surface are responsible for the wettability modification. The properties of<br>the carboxylic material may have influence on the initial wetting conditions and also on the wettability<br>alteration process. In this paper we have extracted water soluble acids from a crude oil with high AN. The<br>original oil (AN=1.8 mgKOH/g) and the treated oil depleted in water soluble acids (AN=1.5 mgKOH/g)<br>were used to study wetting properties and oil recovery by spontaneous imbibition with chalk as the porous<br>medium. The water wetness appeared to be lower for the original oil compared to the treated oil. In a<br>spontaneous imbibition process with wettability modification at 110 °C, seawater imbibed faster into the<br>cores saturated with the treated oil containing no water soluble acids.