Impact of organic acid molecular length and structure on rock oil-wetting rapidity and stability

The oil-wetting properties of organic acids play a crucial role in various industrial applications, including enhanced oil recovery, oil spill remediation, surface modification, and so on. This study investigated the impact of organic acid molecular length and structure on oil-wetting rapidity and stability on sandstone and carbonate. Model oils prepared by dissolving organic acids in n-decane, and crude oil, were used as the oil phase. Their oil-wetting behavior was evaluated by contact angle values. The maximum molecular length of each organic acid was approximated based on its molecular structure. Our results indicate that organic acids change wettability much faster in carbonate rock than in sandstone. Longer organic acid molecules exhibit enhanced oil-wetting potential due to increased hydrophobic interactions with oil phases. Water film does not have a long-term impact on the oil-wetting process by organic acid on Indiana limestone. However, the existence of a water film largely inhibited the oil-wetting process for Indiana limestone in crude oil, and for Berea sandstone in crude and model oil. Furthermore, molecular structure, such as the presence of functional groups, significantly influences oil-wetting properties. Organic acids with an aromatic ring demonstrated a more stable oil-wetness against wettability alteration induced by surfactant treatment. Gemini surfactants with benzene ring(s) in the spacer removed aromatic organic acid more efficiently than surfactants without benzene ring. Overall, this study provides insights into the design and optimization of organic acids for applications requiring effective oil-wetting and oil-wetness stability, as well as the designing of surfactant structures with higher oil removal efficiency.