Pore-Scale Analysis and Visualization of Tertiary Cationic Surfactant Flooding in a Complex Carbonate

We investigate the pore-scale mechanisms of displacement using cationic surfactant dodecyltrimethylammonium bromide (DTAB) flooding as a tertiary enhanced oil recovery (EOR) technique in a complex carbonate rock using high-resolution X-ray microcomputed tomography (micro-CT). A carbonate sample was initially altered to be oil-wet through contact with crude oil, followed by sequential brine and surfactant injection to evaluate the impact on oil displacement and investigate oil recovery mechanisms. We used a concentration of DTAB above the critical micelle concentration, CMC, with no cosolvent. Image-based pore-scale analysis of fluid occupancy, wettability alteration, contact angles, interfacial areas, capillary pressure, and fluid connectivity was performed. The contact angles, mean curvatures, and capillary pressures indicated a transition from oil-wet to a mixed-wet state when we switch from brine to surfactant injection. The results indicate that DTAB flooding reduced interfacial tension and altered wettability, leading to increased oil recovery, particularly from small pores and throats, where brine flooding was ineffective. The results were compared to those of a previous study of secondary DTAB flooding. We hypothesize that wettability alteration was caused by competitive adsorption and hydrophobic interactions, promoting oil detachment from the rock surface. This study demonstrates that DTAB can enhance oil recovery in carbonate formations without requiring ultralow interfacial tension, making it a cost-effective alternative for complex reservoirs.