Effects of Various Solvents on Adsorption of Organics for Porous and Nonporous Quartz/CO2/Brine Systems: Implications for CO2 Geo-Storage

The underground geo-storage of carbon dioxide (CO2) is an essential component of the carbon capture and sequestration value chain. The success of CO2 containment depends on the wetting state of the rock, which controls the mechanism of fluid flow and distribution. The presence of organic acids in the storage formation introduces a considerable effect on the wettability of the rock/CO2/brine system under various temperature and pressure conditions. Despite the previous studies on this topic, the impact of the substrate pores, the rock surface roughness, and the solvents used to prepare the organic acid solution under various temperatures and pressures has not yet been elucidated. In the present study, the contact angles of non-porous quartz and porous Fontainebleau quartz are measured in CO2/brine systems at various pressures of 0.1–20 MPa and temperatures of 298 and 323 K. In addition, various solvents are used to prepare the stearic acid solution in order to assess their influence on the adsorption of organics for porous and non-porous quartz/CO2/brine systems. The results clearly indicate that n-decane is the most effective solvent for solubilizing the stearic acid to attain full wettability of the substrate by CO2 due to its polar compatibility with the stearic acid. Generally, the porous aged Fontainebleau quartz exhibits higher contact angles than the aged non-porous quartz at higher pressures, and the unaged Fontainebleau surfaces demonstrate water wettability, with a wide range of advancing and receding contact angles of less than 90°. However, when the pressure is increased to 15 and 20 MPa in the CO2/brine system, the contact angles of the Fontainebleau quartz are higher than those of pure quartz. These results suggest that the surface roughness of the rock merely amplifies the inherent surface chemistry and original wettability of the rock if surface conditions are hydrophobic.