Wettability alteration of the quartz surface in the presence of metal cations

Experimental research was conducted to clarify the wettability alteration mechanism in the presence of metal cations. Wettability was studied by measuring the contact angle on a quartz-crude oil-water system. The quartz surface is aged in an asphaltene/toluene solution to study the effect of aging time, asphaltene concentration, water film on the quartz surface, and metal cations in the water film on wettability alteration of the quartz surface. The quartz surface property is characterized with ζ-potential measurements and infrared (IR) spectroscopy to clarify the wettability alteration mechanism. Results show that quartz surface becomes more oil-wet with the increase of the asphaltene concentration. The quartz with a pure water film shows less oil-wetting after soaking compared to the dry quartz surface, while the presence of metal cations in the water film can improve oil wettability of the surface. ζ-Potential measurements show that Ca²⁺ and Mg²⁺ compress a diffused double layer of quartz powder more effectively than Na ⁺, which makes asphaltene adsorption easier because of the reduced electrostatic repulsion. IR spectra analysis indicates that asphaltene molecules can interact with hydroxyls on the quartz surface by polar interactions and asphaltene can be absorbed on the quartz surface with ion binding of hydrated divalent metal cations.