Montmorillonite surface properties modifications by asphaltenes adsorption

The effects of asphaltenes on the particle size, and the surface charge of two montmorillonite clays having in water various particle sizes, flow behaviours, and cationic exchange capacities (CEC) are investigated. The aim of this work is to contribute to the comprehension of the mechanism by which the asphaltenes alter the mineral wettability in an oil reservoir. Thus, adsorption of asphaltenes onto clays was made from water-saturated toluene, and the resulting asphaltenes covered clays were dried to remove trace of solvent and then dispersed in water. Upon adsorption of asphaltenes onto various clays, the mineral surface charge is reduced and the aggregation of the clay particles is enhanced, as observed, respectively, by microelectrophoresis and scanning electronic microscopy (SEM). Further, the samples aqueous dispersion properties such as the natural pH and the electrical conductivity were found, in all instances, to be lower for the asphaltenes covered clays as compared to the bare minerals, indicating reduction by asphaltenes of the clay's CEC. It is shown that the asphaltenes adsorption from water-saturated toluene onto clay is higher for the solid mineral having in water and at natural pH, the lower surface charge, the highest particle size and presenting the highest yield point for flowing. (c) 2006 Elsevier B.V. All rights reserved.