Wettability of CO2/brine/clay has an important role in CO2 geo-sequestration efficiency as it highly affects the fluid flow through a porous medium. In this context, it is vital to measure the wettability of the clays. In addition, many previous studies have been conducted to investigate the wettability of pure clay minerals. Thus, in this study, we systematically measured the wettability of a mixture of different clay minerals (i.e. 14 wt% kaolinite, 48 wt% illite and 38 wt% montmorillonite). Both advancing and receding contact angles were measured at four different pressures (ranging from 5 MPa to 20 MPa) and two different temperatures; 305 K and 333 K. Then, for each clay minerals suspension with the brine, the zeta potential analysis was conducted to examine the clay's correlation to macroscopic contact angle. The results illustrate that the advancing and receding contact angles increased with increasing pressure (i.e. the wettability of the mixed clay has been altered from weakly water-wet to intermediate-wet with the pressure increased from 5 to 20 MPa). However, the results show that mixed clay minerals contact angle was a slight decrease with increasing temperature from 305 K and 333 K. Therefore, we conclude that the mixed clay minerals contact angle is highly affected by reservoir pressure and that higher pressures lead to reduce the CO2 storage capacity and contaminate security of the mixed clay minerals. This study has various significant implications for CO2 flow in porous media, CO2 entrapment in the deep geological reservoirs for CO2 geo-sequestration, and CO2 dynamics and spreading in geological formations for CO2 injection of methane recovery.

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