Optimum salinity brine and surfactant interaction with crude oil and carbonated rock at fluid–fluid and rock-fluid interfaces: Evaluating ion-specific effects on the system

Abstract

The smart water injection (SWI) method is derived from low salinity water flooding, which aims to increase oil production. The complexity and heterogeneity of carbonate reservoirs require further investigation. Understanding the active mechanisms during SWI is crucial for designing the injected water composition to enhance the efficiency of the method. However, there is a research gap regarding the dominant factors that influence the performance of SWI, particularly both the ‘fluid–fluid’ and ‘rock–fluid’ interactions, simultaneously. To address this issue, the article through new insight into ions, solutions, and tests tries to enhance the precision of the obtained results by optimizing the solutions by changing the potential determining ions (PDI) in fixed ionic strength through contact angle measurements. Furthermore, by using a cationic surfactant, which has not been previously used in low-salinity water flooding experiments, surfactant-free solutions, and proper tests for each mechanism, including Zeta potential, pH measurements, interfacial tension, vial test, high-resolution microscopy, and Karl Fischer titration, interactions on fluid–fluid and rock-fluid interfaces were tested and investigated. The results were validated through core flood tests. The study found that coordination was observed between multivalent ion exchange and water in oil micro-dispersion, which are two current mechanisms in both micro- and macro-scale media. In surfactant-free solutions, the effect of ions was discerned in the order of SO₄²⁻, Mg²⁺, and Ca²⁺. The formation of micro-emulsions and the IFT reduction by ionic pairs of surfactants significantly increased oil recovery by up to 65%. The effective ions facilitating this performance were ranked as follows: SO₄²⁻ > Ca²⁺ > Mg²⁺.