Effects of salinity, ion type, and aging time on the crude oil-brine interfacial properties under gravity condition

Abstract In this study, the impacts of salinity, ion type, and aging process were investigated on coalescence and spreading of crude oil interfaces (including an oil droplet and an oil film) under gravity, through drop rest time measurement techniques, aided by an image analysis system. Three different salt solutions of NaCl, Na2SO4, and MgCl2 were studied at different ionic strengths, ranged from 1% to 150% of Persian Gulf seawater ionic strength. According to the results, aging the oil droplet in the brine increased the interfacial rigidity. Addition of a gas phase - by thinning the surface oil film - almost doubled both rest time and spreading time values. In the aged mode, the presence of salt in the water phase increased both rest time and spreading time, depending on the salt type and concentration. Increasing salinity, especially in the case of MgCl2 and Na2SO4 salt solutions, resulted in higher interfacial rigidity and lower oil-brine interfacial tension.