Mechanistic Investigation of Wettability Alteration by Bulk and Interfacial Asphaltenes Using a Surface Force Apparatus

Abstract

Asphaltenes play an important role in the wettability alteration of sedimentary rocks; however, the mechanisms of their interactions with mineral surfaces are still an open area of research. In this study, we used a surface force apparatus to probe the intermolecular forces between asphaltene samples and muscovite mica in aqueous media. The samples consisted of bulk asphaltenes (BA) precipitated from a Wyoming crude oil and their interfacial material (IM) subfraction. The impact of the monovalent salt concentration in water was first investigated at ambient conditions. We found that increasing sodium chloride (NaCl) concentration from 0 to 1 wt % resulted in a rise in the steric repulsive forces during the approach of BA and IM films toward a bare mica sheet. In other words, amply saline brines induced a higher salt−asphaltene binding tendency, leading to an increased brush extension and consequently a higher steric repulsion with mica. Forcing the BA into contact and breaking the thin water film on mica gave rise to an adhesive force that increased from 0.75 mN/m in distilled water to 35.1 mN/m in 1 wt % NaCl brine. Similarly, IM demonstrated an increasing repulsion with mica due to the rise in brine salinity, which induced tighter molecular packing with a grafting distance of 8.1 nm in distilled water and 6.4 nm in 1 wt % brine (compared to ∼2 m with BA). This behavior intensified the steric repulsion at the point of contact, and no adhesion of IM was observed on the mica surface under these conditions. To mitigate the adhesion of BA onto mica at high salinities, we explored for the first time the impact of different wettability modifiers on the intermolecular forces involved in these systems. Cationic surfactants such as dodecyl trimethylammonium bromide (DTAB) gradually reduced the adhesion forces from 35.1 to 0 mN/m after 24 h by progressively passivating the polar sites of BA and the negatively charged sites of mica. On the other hand, anionic nanoparticles such as graphene quantum dots (GQDs) instantaneously suppressed the adhesion of BA to mica by hydrogen bonding with the nitrogen heteroatoms of BA. The findings of this study shed some light onto the controlling parameters promoting the wettability alteration of mica by asphaltenes and highlighted the remarkable ability of GQDs to restore this wettability.