Effect of Aqueous-Phase Salinity on the Content and Composition of Asphaltenes Precipitated from Water-in-Oil Emulsions

This study examines the influence of aqueous-phase concentration and salinity on the formation of precipitates in water-in-oil emulsions. Precipitates were isolated from the crude oil and from its emulsions with deionized water and formation waters of varying salinities (52.0–312.6 g/dm3), and then characterized. Water droplets were larger in the emulsions than in the precipitates, and their size depended on the salinity of the aqueous phase. Higher formation-water salinity corresponded to higher asphaltene content and lower resin content in the precipitates, whereas paraffin content remained largely unchanged. The molecular weight of asphaltenes in the precipitates obtained from emulsions with formation waters and deionized water increased significantly compared to that in the parent crude oil. Furthermore, asphaltenes precipitated from formation-water emulsions exhibited higher contents of carboxylic and sulfoxide groups.