Effects of SiO2 Nanoparticles on Wettability and CO2-Brine-Rock Interactions in Carbonate Reservoirs: Implications for CO2 Storage

Nanoparticles effectively enhance the CO2 geological storage capacity by altering wettability during CO2-brine-rock interactions, which significantly impacts the CO2 residual trapping and migration in reservoirs. However, the effect of nanoparticles on CO2-brine-rock interactions in carbonate formations is poorly understood. Therefore, in this study, the impact of SiO2 nanoparticles (SNPs) on CO2-brine-rock interactions was evaluated under supercritical CO2 conditions (60 degrees C and 12 MPa) by analyzing wettability, conducting X-ray diffraction, scanning electron microscopy analyses, measuring weight loss, and performing low-field nuclear magnetic resonance (LFNMR) tests. The results indicated that (a) both CO2-brine-rock interactions and SNPs-CO2-brine-rock interactions can alter the wettability of carbonate rock surfaces from oil-wet to water-wet and that the carbonate rock became more water-wet after SNPs addition; (b) CO2-brine-rock interactions primarily involved the dissolution of calcite in carbonate rocks under acidic conditions, but SNPs-CO2-brine-rock interactions were more intense; (c) based on LFNMR analysis, the pores of the carbonate core in this study were divided into small pores (T-2 < 5 ms) and large pores (T-2 > 5 ms), with CO2-brine-rock interactions occurring mainly in the large pores of the carbonate cores but with enhanced interactions in small pores; (d) CO2 solubility in solution after CO2-brine-rock interactions increased with increasing pressure and eventually reached equilibrium, and this trend was observed both in the CO2-brine-rock system and the SNPs-CO2-brine-rock system. However, the CO2 solubility in the SNPs-CO2-brine-rock system was greater than that in the CO2-brine-rock system.