Adsorption behavior of surfactants on sandstone reservoir rocks with carbonate cements and its influence on wettability alteration

This study investigates the adsorption behaviors of surfactants in sandstone reservoir rocks containing various amounts of carbonate cement/minerals and their impact on wettability alteration under low-salinity conditions. Two types of rock samples from sandstone reservoirs of Assam oilfields in India are selected based on XRD results. These rock types are (i) high carbonate cement (HCC) core sample with higher carbonate cement (calcite 5.6% and dolomite 4.0%), and (ii) low carbonate cement (LCC) core sample with lower carbonate cement (calcite = 0.5% and dolomite 0%). The study reveals that the mineralogy of sandstone reservoir rocks especially the carbonate minerals affects the brine-rock interactions including wettability alternation and surfactant adsorption. Notable differences (2° to 8°) in contact angles for the two rock types at different salinities revealed that carbonate cement in sandstone thus impacts brine-rock interactions. Further, low salinity surfactant (LSS) could positively alter the wettability of both rock types to water-wet conditions (contact angle <60°). The most favorable wettability alterations (up to 30°) were achieved with cationic LSS solutions for both core types. Using LSS solutions also reduced the adsorption of anionic surfactant by around 40% and 33% for HCC and LCC rock samples, respectively. The study's novelty emanates from investigating the impact of sandstone reservoir rock mineralogy with varying amounts of carbonate cements on the adsorption behavior of surfactants under low-salinity conditions. Moreover, this study provides a better understanding of the interrelationship existing between the degree of wettability alteration and the amount of surfactant adsorbed by sandstone rocks.