Effect of water chemistry on asphaltene stabilised water in oil emulsions - A new search for low salinity water injection mechanism

Although most of the investigations report that the injection of low salinity water (LSW) can improve oil recovery, the effect ion content/valency could be more significant than ion concentration in LSW injection. In this study, the impact of aqueous phase ionic strength and ionic content on formation of water microemulsions in model oil with f=0.005 g.g-1 asphaltene content were investigated using state of art petrographic optical microscope. Various salt concentrations of NaCl, CaCl2 and MgCl2 in water are prepared to determine the role of water salinity and ion valency on creation of asphaltene stabilised water in oil (W/O) microemulsions, their stability and morphology. The results reveal that at low ionic strength conditions in presence of divalent cations more W/O microemulsions can be observed. Furthermore, this study shows that the effect of the ion valency of salts on the emulsion stability follows MgCl2 > CaCl2 > NaCl, and Mg2+ plays a crucial role in the stability of water-in-crude oil microemulsions, leading to more stable emulsions in comparison with Ca2+ followed by Na+. These new findings elucidate how large a role, the asphaltene and water chemistry play in the observed W/O microemulsions behaviour in LSW injection.