Asphaltene-Silica Interactions in Salinity Water and Their Ion Dependence

Summary The adsorption of asphaltene on the pore surface not only forms a dense adsorption film but also induces a transition in sandstone wettability to more hydrophobic, which poses challenges to oil displacement, especially in unconventional reservoirs. The asphaltene adsorption exhibits a strong ion dependence, especially toward high ion concentration and high-valence cations, and the mechanism is not yet entirely understood. In this work, atomic force microscopy (AFM), coreflooding experiments, and the self-priming rate method were used to investigate the impacts of ion concentration and types in connate water on the adsorption of asphaltene. Enhanced asphaltene adsorption is observed in the presence of ions, leading to a more pronounced hydrophobic character in the cores saturated by high-salinity water. Then, we proceed with a consideration of the attraction force law between asphaltene and rock. The attraction showed an exponential decay with respect to distance and is in accordance with the hydrated ion bridge interaction. Furthermore, the attraction intensified notably in CaCl2 solution compared to that in NaCl solution and was enhanced progressively with increasing ionic concentration. Therefore, the adsorption amount of asphaltene and ultimately the wettability of the rock are affected by ion concentration and valence in formation water. Our findings hold significant implications for enhancing oil recovery in unconventional reservoirs under high-salinity conditions.