The effect of brine salinity and oil components on dynamic IFT behavior of oil-brine during low salinity water flooding: Diffusion coefficient, EDL establishment time, and IFT reduction rate

Dynamic behavior of fluid-fluid interactions can potentially affect the performance of any enhanced oil recovery (EOR) process including low salinity water flooding. In this work, dynamic interfacial tension (IFT) of crude-oil/brine system is measured in a wide range of salinity of sea water (SW), from 50-time diluted sea water (SW50D) to 2-time concentrated sea water (SW2C). Contrary to the most of published IFT trends in the literature, for the system under investigation here, as the brine salinity increases the crude-oil/brine IFT reduces, which cannot be explained using the existing theories. The lack of a physical model to explain the observed phenomena was the motivation to develop a new model based on a drift-diffusion theory. This theory considers a current of oil polar molecules toward the oil-water interface which is caused by electrostatic attraction from aqueous ions (drift) and a resistance against this current caused by concentration gradient (diffusion). After applying this model to measured dynamic IFT data, the IFT reduction rate, and electrical double layer (EDL) establishment time are calculated. Then, these matching parameters set as criteria to explain the mechanisms behind the dynamic behavior of crude oil-saline water interfacial tension. For further investigation of the involved mechanisms which are responsible for the macroscopic behavior of crude-oil/brine dynamic IFT, the role of oil components is also examined using the IFT reduction rate and EDL establishment time. Although the obtained results show the asphaltene molecules play a vital role in the dynamic IFT behavior, the concentration of n-heptane, in the model oil containing n-heptane and toluene, is essential to capture the IFT behavior of the crude oil. Increasing n-heptane fraction in the model oil to the amount which exist in the crude oil, results in longer EDL establishment time which is in agreement with the crude oil sample.