INTERFACIAL RHEOLOGICAL STUDIES OF EXTRA-HEAVY CRUDE OILS AND ASPHALTENES - ROLE OF THE DISPERSION EFFECT OF RESINS IN THE ADSORPTION OF ASPHALTENES AT THE INTERFACE OF WATER-IN-CRUDE OIL-EMULSIONS

The interfacial behaviour of a crude oil and an asphaltene system has been studied by a planar rheological method. System S1 was a 30% (v/v) xylene dilution of extra-heavy Cerro Negro crude oil; the aqueous pha se was tridistilled water or an NaCl solution (2% (w/v)). System S2 wa s a 3.21% (w/v) dilution of Cerro Negro asphaltene in xylene; aqueous phase as for system S1. These systems were studied under creep in the pH range 1.6-9.5. The elasticity (E0 and E1) and viscosity (eta1, and eta(N)) surface moduli were obtained from creep compliance measurement s. Viscoelastic as well as elastic behaviour was observed. The interfa cial rheological behaviour of asphaltene and crude oil systems was fou nd to be very different in the presence and absence of salt. The high values of the moduli, leading to the high stability of water-in-oil em ulsions, was attributed to flocculation of asphaltene-resin micelles a t the interface. In the absence of resins, asphaltenes were not disper sed and their adsorption at the interface could lead to precipitation and multilayer formation.