An Experimental Investigation of Surface Chemistry of Rocks in the Presence of Surfactants

Surfactant flooding is a well-known chemical enhanced oil recovery (cEOR) technique. However, surfactant surface chemistry and the associated interactions with rock surfaces are complex and have not been fully investigated. Here, we experimentally investigate the surface chemistry of 15 rock surfaces (10 carbonate and 5 sandstones) upon interaction with different types of surfactants, including cationic, anionic, nonionic, and zwitterionic surfactants at different concentrations (before, at, and after the critical micelle concentration, CMC). The rock samples were examined using Scanning Electron Microscopy (SEM) to investigate their structure and surface morphology. To understand the interactions at the surfactant-mineral interface and surfactant behavior, the zeta potential measurements of surfactant-brine-rock emulsions were performed, while surface chemical functional groups were identified by Fourier-transform infrared (FTIR) spectroscopy. The zeta potential results show that both anionic (SDS) and cationic (CTAB) surfactants depict better stability, in carbonates and sandstones, compared to the non-ionic (Triton X-100) and zwitterionic (3- (N, N-Dimethylmyristylammonio) surfactants, which is due to the nature of the charge of each surfactant. Also, the FITR results indicate the existence of different chemical bonds and functional groups at different concentrations for each surfactant type, and the magnitude of these bonds differs as a function of rock type and mineralogy. For instance, the rock samples treated with CTAB cationic surfactant reveal the presence of C-O, Mg-C, and Ca-C groups at all concentrations. However, despite being present at all concentrations, these responses show different magnitudes at different surfactant concentrations. The results of this study provide valuable data set to understand the surfactant surface chemistry interactions with different carbonate and sandstone rock surfaces and thus have direct implications for chemical enhanced oil recovery.