Dual-Functional 2-Methylimidazoline Derivatives for Corrosion and Scale Inhibition in CO ₂ –Containing Aqueous Wellbore Environments

Sweet corrosion and scaling in wellbores have become concomitant challenges associated with the widespread implementation of CO 2 -EOR technology in major oilfields. Although the combined use of corrosion and scale inhibitors is considered an effective strategy to mitigate these problems, it often suffers from limitations such as poor mutual compatibility. Therefore, three novel dual-functional imidazoline-based corrosion-scale inhibitors (ICSIs) were synthesized in this study based on a 2-methylimidazoline backbone, into which sulfonic, phosphonic, and carboxylic acid groups were introduced, namely 2-(2-methyl-4,5-dihydro-1 H -imidazol-1-yl)ethane-1-sulfonate (MIES), 2-(2-methyl-4,5-dihydro-1 H -imidazol-1-yl) ethyl phosphate (MIEP), and 3-(2-methyl-4,5-dihydro-1 H -imidazol-1-yl)propanoate (MIDP). MIEP and MIDP exhibited excellent corrosion inhibition performance with inhibition efficiencies of 85.28% and 85.53%, respectively, in CO 2 -saturated 3.5 wt % NaCl solution at 60 °C on N80 carbon steel. The introduction of phosphonic and carboxylic acid groups increases the number of active adsorption sites on the Fe(110) crystal plane, thereby enhancing the binding strength to the metal surface. The oxygen atoms in MIEP display a uniform charge distribution, while the sulfonate group exhibits a stronger tendency to complex with scale-forming ions, which weakens its adsorption capability and consequently leads to a relatively lower corrosion inhibition efficiency. The introduced scale-inhibiting groups interfere with the active growth planes of CaCO 3 crystals, thereby disturbing their orderly crystallization process. MIEP exhibited the highest scale inhibition performance among the three, achieving a 93.29% inhibition rate at a dosage of only 60 ppm. MD simulations indicated that strong chemisorption occurs between the phosphonic acid groups and the calcite (104) surface, resulting in the superior scale inhibition performance of MIEP.