The effects of pH, acidity, asphaltene and resin fraction on crude oil/water interfacial tension

A basic understanding of the activities of indigenous surfactants of crude oil at the water/oil interface as a function of aqueous phase pH can give us a better insight into the alkaline enhanced oil recovery processes. The present study aimed to elucidate the effect of salinity and crude oil type, specifically the influence of resin and asphaltene molecules during alkaline flooding through interfacial tension (IFT) measurements via pendant drop and spinning techniques. Several model oils containing asphaltene and resin fractions were prepared and their IFTs were compared with those of the original crude oils. Moreover, the elemental analyses of asphaltene and resin fractions were performed, and the total acid numbers of all oils were measured as well. The IFT results of three studied crude oils and the asphaltenic and resinous model oils with sea water and deionized water underlined the importance of the degree of salinity, and qualitative and quantitative nature of resin and asphaltene fractions. It was also revealed that the amount of asphaltene and resin fractions as well as their structural nitrogen and oxygen contents were the most influential parameters on the IFT of crude oil as a function of pH values. In addition, the variations of IFT crude oils/the ionic solution and deionized water were more noticeable in the basic aqueous solutions.