Effect of salinity on the interfacial tension of model and crude oil systems
Date
2012-09-13
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Abstract
It has been observed that the interfacial tension of a hydrocarbon versus water increases with the concentration of salt in the aqueous phase; but when a small amount of surfactant is present in the solution, the interfacial tension decreases with salinity. Crude oil consists of tens of thousands of unknown components, of which many are surface active. It is found in combination with reservoir water, which varies from place to place. The interfacial tension, or IFT, of crude oil is thus a complex function of salinity and surfactant concentration. The objective of this thesis is to study the effects of salinity on the interfacial tension of crude oil.
To complete this study, the following data has been measured using a drop shape analyzer at ambient conditions:
. IFT of pure hydrocarbons, mixtures of pure hydrocarbons, three crude oils of varying density, and a bitumen versus aqueous phases of different salinity. The pure hydrocarbons chosen are toluene, n-heptane, 50 vol. % mixture of n-heptane and toluene (heptol50), and cyclohexane. Salt solutions are sodium chloride, calcium chloride, and sodium sulphate. Salinities were varied between 0 and 15 wt% in water.
. IFT for the same above solutions(except crude oil) with the addition of different surface active materials including sodium dodecylsulphate, cetyltrimethylammonium bromide, a nonylphenol ethoxylate, Triton X-100, 5β-cholanic acid, and asphaltenes.
A model was developed to fit or predict the salinity, solvent, and surfactant concentration for the different mixtures involving pure hydrocarbons. It was observed that a simple model, similar to Gibbs-Langmuir isotherm, was found adequate to fit the data for different surfactants. As expected, the behaviour of ionic surfactants was different from the non-ionic ones. The addition of salt in the solution containing surface active agents altered the distribution of surfactants at the interface due to electrostatic effects and consequently altered the interfacial tension. Such effects were absent in the case of non-ionic surfactants, and was verified experimentally for two non-ionic surfactants.
The results of naphthenic acids and asphaltenes, which are naturally occurring surface active materials found in crude oil, showed that that salinity has a weak effect on the interfacial tension of hydrocarbons versus brine containing these components. The trends of IFT observed for asphaltenes was also seen for crude oil/water system.
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Engineering--Chemical, Engineering--Petroleum
Citation
Kumar, B. (2012). Effect of salinity on the interfacial tension of model and crude oil systems (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/25807