Effect of imidazolium-based ionic liquid on CO2 sequestration: a study on solubility, interfacial properties, and X-ray imaging in water-wet formations

Abstract

The efficiency of geological CO₂ sequestration is often limited by low CO₂ solubility, which poses challenges for long-term storage stability. This study addresses these limitations by exploring the potential of 1-butyl-3-methylimidazolium bromide (BMIM-Br) to enhance CO₂ storage in water-wet subsurface formations. BMIM-Br was synthesized via a microwave-assisted method and the structure was confirmed using different spectroscopic methods including Fourier Transform Infrared Spectroscopy (FTIR), and Proton Nuclear Magnetic Resonance (¹H NMR) analysis.

Under conditions of 3 MPa and 323.15 K, the solubility of CO₂ in a 5 wt% BMIM-Br solution was more than double the solubility in pure water. At 0.3 MPa, the interfacial tension (IFT) between CO₂ and the BMIM-Br solution decreased from 36.3 mN/m to 32.9 mN/m at 293.15 and 323.15 K, respectively compared to the pure water values 69.9 mN/m and 63.8 mN/m respectively at the same conditions. When CO₂ was injected into a Bentheimer sandstone rock sample fully saturated with the aqueous phase. There was a significant increase in CO₂ saturation (S_CO2), rising from 0.58 with pure water to 0.72 with BMIM-Br. The lowered interfacial tension allows more of the pore space to be accessed at the same imposed capillary pressure. When the aqueous phase was injected to displace CO₂, the residual saturation was 0.21 with pure water, but only 0.16 for the BMIM-Br solution. This is likely a consequence of increased dissolution of CO₂ in BMIM-Br. These results suggest that BMIM-Br significantly improves CO₂ solubility and injectivity by reducing interfacial tension. Its overall impact points to a promising strategy for optimizing CO₂ sequestration in subsurface formations.