Role of ammonium in CO₂ mineralization and enhanced oil recovery

This study presents a novel ammonium-assisted surface treatment strategy that couples CO₂ mineralization with smart water (SW) injection for carbonate reservoirs, enabling simultaneous carbon utilization and enhanced oil recovery (EOR). Produced water (PW) was modified with ammonium at 0.1, 0.3, and 0.6 wt%, followed by CO₂ injection and subsequent NaOH addition to induce mineral precipitation and generate treated smart-water formulations. The results show that ammonium dosage governs the trade-off between CO₂ uptake, carbonate mineral formation, and oil recovery performance. The 0.6 wt% formulation (SW-6A) exhibited the highest CO₂ uptake (10.8 g/L) and produced a predominantly carbonate-rich precipitate, with calcite accounting for over 90% of the solid phase and the total carbonate fraction (calcite + aragonite) reaching 96.5%. In contrast, the 0.3 wt% formulation (SW-3A) produced the most carbonate-rich precipitate, with a total carbonate fraction of 97.8% (83.7% calcite + 14.1% aragonite). The 0.1 wt% formulation (SW-1A), despite its lower CO₂ uptake of 4.4 g/L and lower total carbonate fraction of 64.6%, delivered the highest oil recovery (21.8%). These results demonstrate that maximizing CO₂ uptake and carbonate precipitation does not necessarily maximize recovery. Instead, the best EOR performance was obtained at lower ammonium concentration, where the treated brine more effectively modified interfacial properties and wettability in favor of spontaneous imbibition. The study reveals a tunable dual-benefit system in which higher ammonium dosage favors carbon locking through carbonate mineralization, while lower dosage favors oil recovery enhancement, thereby providing a flexible pathway to integrate CCUS with SW-based EOR.