Wettability Alteration of Mineral Surface during Low-Salinity Water Flooding: Role of Salt Type, Pure Alkanes, and Model Oils Containing Polar Components

Low-salinity water injection is an emerging enhanced oil recovery technique and an area of active research. According to many researchers, the role of brine salinity has been attributed to its ability to change the reservoir rock wettability. The influence of different parameters such as total dissolved solids, concentration of individual ions, oil composition, lithology, acid and base number, etc., has been tested previously using different combinations of crude oil and reservoir core samples. However, because of the complex nature of crude oil brine rock system, there is no clear idea of the mechanism of wettability alteration and the influence of above parameters on this process. In this work, we have investigated the governing factors affecting the wettability of mineral surface using pure alkane liquids and model oils (containing organic acid and base). The wettability studies were performed through contact angle measurements over a wide range of concentration (1 mM to 1M) of monovalent and divalent salts (NaCl, CaCl2, and Na2SO4) to identify the effect of salt types and concentrations of different ions present in the injection water. The use of model systems provided a better understanding of the wettability alteration mechanism, in comparison to the earlier studies performed using crude oil and actual reservoir rock sample. The results of this study showed that the wettability alteration with brine salinity is significantly different for pure alkanes and model oils containing polar component, and it is dependent on the type of cations (monovalent versus divalent) present in the system. Scanning electron microscopy and electron dispersive spectroscopy studies showed that the polar oil components such as petroleum acids and bases get adsorbed on mineral (quartz) surface in the presence of cations and are primarily dependent on the cationic concentrations in water, affecting the performance of a low-salinity water flooding process.