Dual-functionality of CO2-responsive ionic liquids for CO2 storage: Fatty acid particles re-precipitation and clay swelling inhibition

Gas channeling during CO2 flooding presents a significant challenge to the effective underground storage of CO2. This study introduces a novel gas channel blocking strategy using the phase transition properties of fatty acid based CO2-responsive ionic liquids (ILs). The ILs were synthesized from choline hydroxide (Ch) and high-melting-point fatty acids (FA), including myristic acid (C14) and palmitic acid (C16), named FA-Ch ILs. These ILs demonstrate phase transformation behavior after CO2 injection, leading to the precipitation of FA as solid particles. The FA-Ch ILs aqueous solution exhibits low viscosity, ensuring excellent injectivity for oilfield applications. After CO2 injection, the precipitated FA particles act as gas channeling plugging agents, while the protonated Ch ions effectively inhibit clay swelling to enhance oil recovery with a synergistic effect. Structural properties and interaction mechanisms of the FA-Ch system were characterized by FT-IR, 1H NMR, and molecular dynamics simulations. The particle size of the FA precipitates was regulated by adjusting FA-Ch concentration and CO2 injection rate to make it suitable as a profile control agent. Furthermore, Ch+ ions demonstrate clay swelling inhibition comparable to traditional inhibitors like KCl. This dual-functionality positions FA-Ch ILs as an innovative solution for addressing gas channeling and clay swelling in CO2 flooding, offering a cost-effective and environmentally friendly alternative to conventional methods.