Carbon management with n-butyl-amine-tuned smart water: Coupling CO₂ mineralization and enhanced oil recovery

Decarbonizing subsurface operations requires injection fluids that can simultaneously immobilize CO₂ and enhance oil recovery (EOR). This study demonstrates the dual functionality of n-butyl amine (n-BA) in a seawater-based workflow that couples CO₂ mineralization with EOR. Arabian Gulf seawater was modified with n-BA (0.3, 0.6, and 1.0 wt%), carbonated with CO₂, and subsequently alkalinized with NaOH to generate smart-water formulations. Increasing n-BA concentration enhanced CO₂ solubility and total inorganic carbon (TIC), promoting divalent-ion removal (Ca²⁺ and Mg²⁺) and precipitation of stable carbonate phases, including aragonite with a maximum solid yield of 9.5 g/L at 1.0 wt% n-BA (SSWBA10). Interfacial measurements reveal that mineralization-induced brine reconditioning alters surface charge and capillary forces: contact-angle and zeta-potential analyses show a systematic transition from oil-wet to water-wet conditions. At low amine dosage, SSWBA3 (0.3 wt%) achieved the highest oil recovery (40%), driven by the lowest interfacial tension (IFT, 3.9 mN/m) and strong electrostatic repulsion between negatively charged oil components and near-neutral rock surfaces, which weakened oil adhesion and facilitated detachment. In contrast, higher n-BA concentrations maximized carbonate locking and wettability alteration but increased interfacial stability. These results demonstrate a tunable trade-off, wherein n-BA concentration governs whether CO₂ mineral sequestration or IFT-controlled oil mobilization dominates, enabling customizable smart-water design for integrated carbon management and EOR.