Imaging emulsions: The effect of salinity on North Sea oils

A workflow to quantify emulsification in water-in-oil (W/O) systems by means of optical microscopy has been applied to study the effect of salinity on emulsification with addition of KCl solutions with increasing concentration to a crude oil sample. A second order relation between droplet size and salinity has been observed for KCl. The effect of the addition of a different salt (NaCl) has also been studied, thereby monitoring the relation between droplet size and the size of the cation. For KCl the droplet size increases up until 5 w% after which it decrease; for NaCl the behaviour is opposite. The effect of interfacially active material isolated from the crude sample has been tested, and the droplet size is substantially affected, with the formation of droplets of considerably smaller diameter. We propose that this observation is due to the presence of two regimes: one where the droplet motive is strongly impacted by cation intercalation in the micellar structure (large droplets) and one where the anions determines the outcome by binding to the surfactants (small droplets).