Relation between brine-crude oil-quartz contact angle formed on flat quartz slides and in capillaries with brine composition: Implications for low-salinity waterflooding

A good understanding of surface wetting is of significant important for Enhanced Oil Recovery (EOR) technologies especially low salinity waterflooding (LSWF), in which wettability alteration of rock surface was considered as the leading mechanism even though the reasons behind have not been conclusively revealed. To further investigate the effect of brine composition (salinity, ion types and valence) on surface wetting at pore level, the attention of this work was given to the brine-crude oil-quartz contact angles formed on flat quartz slides and in capillaries (r = 0.1–0.5 mm), and also to the relation between these two types of contact angles. The results showed that the dependence of the flat slide contact angles on brine composition was different from that in capillaries, and pore radius needs to be considered in wettability determination in porous media. In capillaries, the formed contact angles were found to decrease with the decrease in capillary radius. Moreover, the flat slide contact angles were slightly larger than the capillary contact angles for a given system but the relationship between these contact angles varied with salt type. In summary, it is believed that pore contact angles should be more appropriate to represent the wettability of a reservoir.