Effect of Acid Number on the Electrokinetic Properties of Crude Oil during Low-Salinity Waterflooding

Understanding crude oil/brine interface chemistry is essential to elucidating the effect of low salinity waterflooding (LSWF) on enhanced oil recovery (EOR). The acid and base functional groups in crude oil result in an electrostatic interaction with the rock’s surface, thereby affecting wettability conditions. Moreover, the content of carboxyl acid components is a key factor influencing electrostatic interaction during LSWF. In this study, the number of carboxyl groups in four different crude oils with varying acid number (AN) was estimated using a combination of zeta potential experiments and a triple-layer surface complexation model. In addition, the surface complexation modelling parameters for the dissociation of carboxyl groups and the adsorption of calcium and magnesium ions were also determined. The experimentally determined parameters and carboxyl groups sufficiently predicted the crude oil/brine interface at high and low salinities of seawater and formation water. The density of carboxyl groups ...