Carbon Dioxide/Brine, Nitrogen/Brine, and Oil/Brine Wettability of Montmorillonite, Illite, and Kaolinite at Elevated Pressure and Temperature

Wettability of CO ₂ /brine/clay is one of the most important parameters in assessing CO ₂ storage capacities and containment security. Despite its importance, the literature data in this context are very limited. We thus systematically measured montmorillonite, illite, and kaolinite wettability for CO ₂ /brine, nitrogen/brine, and nitrogen/oil systems at various pressures (5, 10, 15, and 20 MPa) and temperatures (305 and 333 K). The zeta potential of each clay mineral was also measured to investigate its link to the macroscopic contact angle. The results show that both advancing and receding water contact angles for CO ₂ /brine, nitrogen/brine, and nitrogen/oil systems increase with an increase in pressure. However, they are only slightly reduced by increasing temperature. It was also shown that montmorillonite has a higher water contact angle in the presence of CO ₂ , followed by illite and kaolinite. The same trend was measured for nitrogen/brine and brine/oil systems. Consequently, montmorillonite is strongly oil-wet; kaolinite and illite, however, are strongly water-wet at typical storage conditions (high pressure and elevated temperature). This has important implications for CO ₂ geostorage in determining the flow of CO ₂ and its entrapment, fluid spreading, and dynamics in the reservoir.