Evaluating the role of salts on emulsion properties during water-based enhanced oil recovery: Ion type, concentration, and water content

Potential determining ions (SO42 , Mg2+, Na, and Ca2+) positively affect oil recovery. These ions can cause changes in the oil and water system due to their ionic radius and proper charge density. Besides the type of ions, the concentration of these ions is also important. In order to maximize oil recovery, the concen-tration of these active ions should be at a level that pulls the polar components of the oil towards the oil- water interface and causes the interfacial tension to decrease, resulting in a decrease in capillary force and an increase in oil recovery. In some cases, the presence of various ions in the formation water or injection water provides the conditions for the formation and stability of the emulsion. Emulsion forma-tion sometimes reduces production and sometimes improves production from oil reservoirs. Therefore, it is imperative to study the effects of ions on the formation, stability, and viscosity of emulsions. Regarding the emulsion stability in the presence of different ions, there are high uncertainties, and there is no uni-form opinion on this matter. In this study, MgCl2, CaCl2, NaCl, and Na2SO4 were used to investigate emul-sion properties. Droplet size and viscosity were measured using an optical microscope and a rolling ball viscometer, respectively, in order to determine emulsion stability. The results have shown that salts with higher positive charge density, such as MgCl2 and CaCl2 can significantly reduce the size of emulsion dro-plets and increase emulsion stability. Moreover, the presence of divalent anions such as sulfate reduces the amount of asphaltene at the interface between oil and water, thereby reducing the stability of the emulsion. In the order of MgCl2 > CaCl2 > Na2SO4 > NaCl, salts decreased the droplet size and increased the emulsion stability. The viscosity of the emulsion also showed a similar trend, as the average particle size decreases, the viscosity of the emulsion increases. Based on the results, the size of the emulsion dro-plets decreases up to a certain concentration and then increases. In the case of all salts, this concentration was equal to 10,000 ppm. The viscosity of the emulsion shows an increasing trend up to the concentra-tion of 10,000 ppm, and after this concentration, it shows a decreasing trend. Salt-in and salt-out effects are responsible for the reduction and increase in droplet size. This study can provide insight into the effect of different ions on the stability and viscosity of the emulsion, as well as the design of the injection fluid for the enhanced oil recovery process. (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

Potential determining ions (SO42 , Mg2+, Na, and Ca2+) have a positive effect on oil recovery by causing changes in the oil and water system. The concentration of these ions, in addition to their type, is important for maximizing oil recovery. The presence of various ions in the formation water or injection water can affect emulsion formation and stability, which in turn affects oil production. This study investigates the effects of different ions on emulsion properties and provides insights for the design of injection fluids in enhanced oil recovery processes.