Adsorption Mechanisms of a Novel Cationic Gemini Surfactant onto Different Rocks

The need to reduce surfactant adsorption on rock surfaces has been a difficult task in chemical enhanced oil recovery, as it directly impacts the economics of the project. This requires a comprehensive insight into the adsorption mechanism on rocks. The adsorption mechanism of an in-house cationic gemini surfactant on different rocks has been studied in this work. The novel surfactant is compatible with high temperature and high salinity environments. All experiments were conducted at room temperature and in deionized water. Adsorption in sandstone rocks was found to be significantly higher than that in carbonates because of the high density of negative charges. The differences in the quantity of the adsorbed surfactant can be explained by different layer structures. It is proposed that an interdigitated bilayer is formed on carbonate rocks, whereas a noninterdigitated bilayer is formed in sandstone rock samples. The maximum and minimum adsorption values were found to be around 9 and 1 mg/g-rock in sandstone and carbonates, respectively. Scanning electron microscopy showed that the surface of sandstone rocks was rougher after the adsorption of the gemini surfactant, whereas no substantial variation in the morphology of carbonates was found. Similarly, Fourier transform infrared spectroscopy showed the symmetric and asymmetric vibration of the CH₂groups in the post-adsorption analysis of sandstone but not in carbonates. Adsorption isotherm modeling was also conducted to investigate the adsorption mechanism of the gemini surfactant on different rocks. All rocks follow a Hill isotherm, showing that the adsorption process is cooperative. However, better curve fitting was obtained using a Redlich-Peterson isotherm in sandstone, whereas both the Langmuir and Redlich-Peterson isotherm performed better for carbonates. The experimental results confirm the formation of interdigitated and noninterdigitated bilayer of the employed surfactant, which explains its adsorption behavior in different rocks and how this adsorption follows different adsorption models in different rocks.