Designing Injection Water for Enhancing Oil Recovery from Kaolinite Laden Hydrocarbon Reservoirs: A Spectroscopic Approach for Understanding Molecular Level Interaction during Saline Water Flooding

Numerous experiments were performed to understand the mechanism(s) behind incremental oil recovery from hydrocarbon reservoirs during low saline water flooding (LSWF). It is believed that the roles of clay minerals present in the hydrocarbon reservoir rocks and the salt concentration in the injected water have a significant effect on the oil recovery during LSWF. Yet, the exact interaction mechanism(s) is still doubtful for designing injection fluids for enhancing oil recovery from subsurface reservoirs. For understanding the interaction between reservoir components explicitly, kaolinite and crude oil, and the interaction between reservoir components and injection saline water, three dead crude oil samples collected from different reservoirs of Cambay basin, India, and two kaolinite powder samples were used in this study. The kaolinites are different on the basis of their exchangeable cations, Fe³⁺ substitution in octahedral sites, and cation exchange capacity (CEC) values. The three crude oils show differences regarding asphaltene content and the abundance of polycyclic aromatic hydrocarbon in asphatenes. The interaction between reservoir components, particularly, kaolinite and crude oil, was demonstrated by keeping both the kaolinite and crude oil mixtures for two months. Detailed analysis of X-ray diffraction patterns, Fourier transform infrared (FTIR) spectra, and CEC values indicated that the polar oil components are adsorbed onto the interlayer surfaces of kaolinite, making it oil wet, and the interaction depends highly upon the composition of kaolinite and crude oil. The oil removal capacity of three brine concentrations of 500 (low saline), 3000 (intermediate saline), and 8000 ppm (high saline) of NaCl, CaCl₂, and MgCl₂ from oil adsorbed kaolinites was investigated using UV–visible and fluorescence spectroscopy techniques. The present study demonstrated that low saline water (500 ppm) rich in Na⁺ ion is more capable of desorbing the maximum amount of 4–6 ring size polycyclic aromatic hydrocarbon (PAH) components from kaolinite interlayer surfaces with respect to Ca²⁺ and Mg²⁺ ions. The composition of polar oil components, particularly, asphaltenes enriched with 4–6 ring PAH, greatly influences the recovery of oil from a mixed wet to oil wet kaolinite laden hydrocarbon reservoir during saline water flooding. Thus, apart from the concentration level of the saline water, the type of cation present in the saline water plays the major role during LSWF. The kaolinite composition, its crystallinity, and ring size of PAH in asphaltenes present inside a hydrocarbon reservoir also influence the enhanced oil recovery (EOR). These molecular level insights are valuable for designing effective injection fluids for enhancing oil recovery during LSWF in kaolinite laden hydrocarbon reservoirs.