Wettability alteration of kaolinite exposed to crude oil in salt solutions

Adsorption and deposition of polar components of crude oils onto kaolinite in the presence of aqueous solutions of sodium and calcium chlorides is probed by spectroscopy, microscopy and drop contact angle. The fine kaolinite particles are thinly coated onto glass to remain immobile during the aging in salt solution and oil, and subsequent solvent rinsing. These thin coats facilitate quantification of the extent of deposition versus salt composition, while also allowing high-resolution microscopy of its spatial distribution. The asphaltene-based deposits take the form of nanoparticle aggregates decorating kaolinite faces and edges. At low salinity and low-neutral pH, water surrounding kaolinite is expelled by oil deposition and pore penetration to strongly alter wettability of the aggregate from hydrophilic to oleophilic, and trends are in qualitative agreement with expectations from DLVO theory. Higher ionic strength suppresses oil deposition, either by limiting it to kaolinite edges in the case of sodium chloride-rich solutions or protecting both faces and edges at high calcium chloride contents. Only the latter suffices for the kaolinite aggregate to substantially retain its hydrophilicity.