Comprehensive Rheological Characterization of Imidazolium-Based Ionic Liquids for Enhanced Oil Recovery

Oil and gas remain the primary energy sources globally, even with advancements in renewable energy technologies. Significant oil deposits remain unrecovered after conventional extraction methods. Chemical enhanced oil recovery (EOR) effectively recovers bypassed and residual oil. However, conventional surfactant flooding faces challenges, including instability, high adsorption, and environmental damage, reducing oil recovery efficiency and profitability. This research proposes using benign ionic liquids (ILs) that exhibit high emulsification and electrostatic stabilization at elevated salinity and temperature. Therefore, this study aims to analyze the rheological (flow and deformation) characteristics of Emirati light crude oil and its emulsions for EOR. The addition of four imidazolium-based ILs—C₁₀mimCl, C₁₂mimCl, C₁₂mimBF₄, and C₁₆mimBr—diluted in seawater (SW) and formation brine (FB) was examined at 500 ppm. Additionally, the effects of the IL carbon chain length, salinity, anion type, temperature, shear rate, time, and angular frequency were studied. The prepared emulsions exhibited high stability, reduced viscosity, and shear-thinning behavior, which were accurately characterized by the power law. Furthermore, viscoelastic properties were measured, including storage modulus (G’), loss modulus (G"), crossover frequency, and damping factor (tan δ). Longer alkyl chain ILs, such as (FB-C₁₆mimBr), exhibited the earliest crossover frequency of 13 rad/s and achieved the lowest emulsion viscosities of 1.73 mPa·s and 0.71 mPa·s at 25°C and 80°C, respectively, measured at 1000 s⁻¹. This results from their increased hydrophobicity and ability to disrupt hydrogen bonds between asphaltene molecules. Overall, these findings indicate that ILs—as green alternatives to conventional surfactants—improve the rheological properties of oil emulsions by lowering viscosity, enhancing flowability, and increasing stability while ensuring uniform oil displacement, making them effective for EOR.