Toward mechanistic understanding of natural surfactant flooding in enhanced oil recovery processes: The role of salinity, surfactant concentration and rock type

Surfactant flooding has emerged as an interesting enhanced oil recovery (EOR) process due to wettability alteration and reduction of oil-water interfacial tension (IFT). Environmental concerns and high cost, cause synthetic surfactant flooding to become expensive and uneconomical in some circumstances. Natural surfactants are environment-friendly and less expensive than synthetic surfactants which recently have been proposed as alternatives for synthetic surfactants in EOR processes. However, the exact mechanism behind natural surfactant flooding as EOR process is an unsettled and complex issue that has not been completely understood. In this communication, the use of natural surfactants as an alternative for synthetic surfactants for wettability alteration of oil-wet rocks in EOR processes was investigated. Through the wide range of experiments, the performance of a natural surfactant named Cedar in the wettability alteration of carbonate and sandstone rocks was deeply studied. Moreover the effect of natural surfactant on oil-water interfacial tension was compared with common used synthetic surfactants. The results showed that Cedar is very efficient in wettability alteration of both carbonate and sandstone rocks and its effect is comparable with common used synthetic surfactants. In addition, it was found that the cationic surfactant is more effective than anionic surfactants in wettability alteration of carbonate reservoirs. On the other hand, the anionic surfactants are very effective in sandstone rocks. In addition, two distinct trends were observed for wettability alteration of surfactants at different salt concentrations. When the head of surfactant and rock surface carries the same charge, there is an optimum salinity for wettability alteration. Finally, the core flooding experiments demonstrated that natural surfactant can increase oil recovery efficiently.