Influence of Oil-Wet Wettability and Nanoparticle Treatments on Carbonate Rock Dissolution and CO ₂ Leakage Risk in Saline Aquifers

Wettability plays a critical role in governing CO2 trapping mechanisms and geochemical interactions in saline aquifers. However, the influence of surface wettability on carbonate dissolution under CO2-rich conditions remains underexplored. This study investigates how oil-wet and nanoparticle-treated surfaces impact mineral dissolution, pore structure evolution, and leakage risk in carbonate formations. Controlled experiments were conducted on limestone core samples modified to three wettability states: untreated (water-wet), silica nanoparticle-treated, and oil-aged (CO2-wet). The samples were exposed to CO2-saturated brine at 1600 psi and 60 °C for 3 weeks. Postreaction characterizations included contact angle measurements, scanning electron microscopy (SEM), BET surface area, ion chromatography, and porosity–permeability analysis. The untreated sample exhibited the highest mineral loss (0.40%) and the greatest porosity (2.36%) and permeability (29.53%) increases, indicating intense dissolution and pore network reorganization. Silica-treated rocks showed partial protection, with 0.26% mass loss and moderate enhancement in flow properties. In contrast, the oil-aged sample retained nearly all mass (0.03%), with minimal structural change, reflecting the stability of the hydrophobic barrier. SEM images confirmed distinct patterns of surface degradation aligned with wettability. Complementary aqueous ion analysis revealed that Ca2+ and Mg2+ release in untreated samples were 3-fold and 2-fold higher, respectively, than those in the nanoparticle-treated samples. Contact angles increased from 125.7° to 145.6° (untreated) and from 144.5° to 156.2° (silica-treated), indicating stronger water-wet behavior after CO2 exposure. These findings highlight the importance of tailoring surface conditions to balance CO2 trapping efficiency with rock integrity in carbonate geological storage systems.