An investigation of the correlation between interfacial properties and phase composition in the crude oil/water system

Enhanced oil recovery can be obtained by flooding the reservoir with chemical fluids. However, complex interactions between the crude oil components, floodwater composition and reservoir rock minerology have to be comprehended in order to exploit the potential efficiency of these techniques. This thesis will focus on the effect of varying the water composition on the crude oil/water interfacial tension. The pendant-drop method was utilized for dynamic interfacial tension measurements, where the equilibrium interfacial tension was estimated by two different calculation-methods. The aim of this investigation has been to inspect whether differences in interfacial activity can be related to differences in the composition for two medium density crude oils, both retrieved from the North Sea. Organic analysis techniques imply that one of the crude oils is highly acidic and biodegraded, while the other oil is high in asphaltene content. Multivariate analysis methods have been utilized in order to develop an experimental plan and to identify the most significant variables at different conditions. At simulated reservoir conditions, i.e. pH close to neutral, both crude oils' interfacial activity showed relatively low variance with respect to changes in ionic strength and concentration of divalent ions. At caustic conditions, it was discovered that the emulsion stability increased drastically for the acidic oil dispensed in water at low ionic strength and in the absence of divalent ions. Addition of Ca^2+ completely eliminated the high interfacial activity. Furthermore, it was found that the crude oil with the higher asphaltene concentration reacted completely different at these conditions, and did not form stable emulsions. To the contrary, high water phase ionic strength promoted drastic changes in the crude oil's consistency. Overall, pH appeared to be the most efficient promoter for reductions in the interfacial tension. The variance in crude oil acidity and asphaltene concentration was hypothesized to be the main sources of observed differences in interfacial activity