Reactive Transport Modeling and Experimental Evaluation of Formic and Acetic Acid for Mitigating the Coupled Effect of Salt Precipitation and Fines Migration in CO2 Storage Systems

Abstract

Abstract Injectivity impairment due to the coupled processes of salt precipitation and fines migration continues to limit the efficiency and reliability of geological CO2 storage, particularly in saline formations where cyclic brine vaporization and mineral destabilization profoundly alter pore-scale structure. Although individual mechanisms of halite (salt) precipitation and fines mobilization are well documented, far less is understood about their synergistic behaviour under scCO2 exposure and, importantly, how targeted geochemical interventions can reverse the damage they cause. This study integrates controlled batch aging experiments with 1-D reactive transport modelling to evaluate the capacity of formic and acetic acid to dissolve salt–fines aggregates, restore pore accessibility, and modify mineralogical reactivity pathways relevant to injectivity recovery. In this study, Berea sandstone cores were aged under scCO2 at brine salinities of 3, 10 and 17 wt% to induce evaporative salt deposition, clay destabilization, and fines entrapment. Post scCO2 aging, mass changes, FESEM observations confirm the formation of mixed salt–clay accumulations (co-precipitation) that wedge and bridge pore throats, reduce pore connectivity, and create preferential blockage zones which were identified as injectivity reducing zones. Mineralogical characterization demonstrates that the severity of coupled damage increases with salinity and is amplified in samples with smaller effective pore apertures. Subsequent treatment with formic or acetic acid initiates dissolution of evaporites and destabilizes bound salt–fines clusters, reflected in net mass reduction and visible modification of pore-wall morphology. Reactive transport simulations in PHREEQC were used reproduce the observed pH evolution and quantify elemental fluxes and mineral reaction rates during both aging and remediation. The simulations identify illite, biotite, and kaolinite as the dominant contributors to Si–Al cycling during acid exposure, while ferric phases dissolve to release Fe exclusively as Fe2+ under the acidic–reducing conditions imposed. Acetic acid generates a more pronounced release of aluminosilicate-derived species, consistent with stronger breakdown of clay edges and interlayers; however, this increased reactivity also drives earlier onset of secondary kaolinite precipitation, indicating a kinetic threshold that may limit its long-term benefit. Formic acid produces more moderate dissolution, with reduced secondary precipitation risk, though its capacity to fully remove salt–fines composites is comparatively lower. Together, the experimental and modelling results demonstrate that weak organic acids can partially reverse the multi-mechanism damage induced by scCO2, but their effectiveness is governed by the interplay between dissolution kinetics, secondary mineral stability, acid strength, and brine chemistry. The findings establish a mechanistic basis for tailoring organic-acid treatments to specific reservoir conditions and highlight the need to balance aggressive evaporite dissolution with the risk of re-precipitating clay minerals that can re-impair injectivity. This integrated framework provides a novel pathway for designing more reliable remediation strategies in CO2 storage operations experiencing coupled salt precipitation and fines migration.