Dynamic adsorption of asphaltenes on quartz and calcite packs in the presence of brine films

The adsorption of asphaltenes on mineral surfaces in the absence of brine has been extensively studied in the past. However, brine is often present in reservoir formations and remains in porous media after drainage by oil as a continuous film of various thicknesses. The presence of a thick brine layer on the mineral surface can act as a mechanical barrier between asphaltenes and the mineral and therefore hinders the adsorption. On the other hand, a thin brine film (less than 100 nm thickness) can rupture under favorable conditions and allow asphaltenes to directly adsorb on the mineral surface. The stability of thin brine films and hence the amount of asphaltene adsorption depends on the nature of asphaltenes, the type of minerals in the rock, and the brine chemistry. This study investigates the dynamic adsorption of asphaltene-in-toluene solutions on packs of wet quartz and calcite. Unlike quartz, calcite is very reactive in aqueous media and can dissolve or precipitate under certain conditions. To the best of our knowledge, this is the first study of asphaltene adsorption on calcite packs in the presence of brine and under flow conditions. All experiments were performed on mineral packs with comparable mesh sizes and porosities and containing an irreducible brine saturation of about 15%. A UV-vis spectrophotometer was used to monitor the outlet concentration of asphaltenes. The effect of brine chemistry (ion concentration, type, and valency) on the dynamic adsorption of asphaltenes on quartz and calcite was systematically studied. Different adsorption trends were observed with quartz and calcite and explained on the basis of the surface forces involved in the stability of thin brine films. The results of this study can help to understand the complex wettability behavior of carbonate reservoirs. (C) 2013 Elsevier B.V. All rights reserved.