Wettability alteration of carbonate rocks during surfactant flooding

Considerable world’s oil reserve is accumulated in naturally fractured carbonate reservoirs, with very low oil recovery efficiency because of their wettability and tightness of the matrixes. The recovery efficiency will be improved considerably if the reservoir rock wettability is changed from mostly oil-wet to water-wet to enhance water imbibition into the oil saturated rock. In this experimental study, an extensive mechanistic study is performed utilizing different analytical tools to study the effects of different surfactnts on the sample rock’s wettability. The results indicate that the surfactants act at different manner according to their structure. Cationic surfactant, C12TAB, desorbed irreversibly stearic acid from dolomite surface via ionic interaction. Nonionic surfactant, TritonX-100, adsorbed on the surface by polarization of π electrons and ion exchange. The released stearic acid adsorbed on the new layer on the surface through hydrophobic interaction. Anionic surfactant, SDS, adsorb on the surface via hydrophobic interaction between the tail of surfactant and the adsorbed acid so change the wettability of surface to neutral wet condition.