Theoretical Approach to the Investigation of Films Occurring at Crude Oil-Water Interfaces

Abstract

Published in Petroleum Transactions, AIME, Volume 219, 1960, pages 350–353. Abstract Recent evidence has indicated that the films forming at crude oil-water interfaces are the result of naturally occurring surface-active components in the crude oil rather than oxidation products resulting from exposure of the oil to air. Since the presence of such films may strongly affect the displacement of oil from porous media, a knowledge of their composition and formation is of fundamental importance. In this study, without the assumption of a specific mechanism, film formation is considered to involve the transfer of a weakly surface-active species in solution in the oil to the oil-water interface. The film gas law and the Gibbs adsorption equation may thus be applied to the system. The rigid films which form upon decrease of the oil-water interfacial area are considered a result of the very slow rate of re-solution of the film material into the oil. When the shrinkage of the interface is very rapid, the amount of film material leaving the interface is negligible, and the system may then be treated in the same manner as an insoluble film. The combination of these treatments leads to a new concept of the film factor in which it may be quantitatively related to the concentration of film-forming material at the interface. Suitable experiments can then yield the following information.Original concentration of surface-active species in the oil.The change of concentration with time.Concentration of surface active species at the interface.The change of this concentration with time.Interfacial tension of the System at any time and its variation with time.Equilibrium concentrations for a given set of conditions.Concentration requirements for solid film formation.Molecular diameter of the adsorbed species. These calculations may be made solely from data taken from measurements on the original oil.