The subsurface processes of enhanced oil recovery (EOR) and carbon capture and storage (CCS) involve complex geochemical interactions mainly CO2, brine, and reservoir rock. This interaction is time-dependent and could influence the wettability and thus the multiphase flow. Less attention has been given to this interaction caused by a weak acidic environment to understand the wettability of CO2/brine/rock systems under high pressure and high temperature over time. This study aims to experimentally investigate the wettability of sandstone and carbonates in a CO2/brine environment at pressure levels between 0.1 to 10 MPa and at 50°C temperature. To this end, a 2-week time duration was considered for aging samples at 50 °C and 10 MPa, for contact angle measurements on theCO2/brine/rock system. The results indicate a significant contact angle shift from weakly water-wet to weakly CO2-wet as a result of geochemical interaction. Particularly, the change in contact angle in carbonates is much higher than the contact angle noticed in sandstone. In addition, there is an increase in contact angle with the pressure, which is consistent with the interfacial tension measurement. Interestingly, the retention of brine on the rock surface shows interesting results in the presence of CO2 – less in sandstone than more in carbonates. This research would help us better understand changes in wettability and thus develop more effective strategies for storage prospectives. In addition, more data is needed to acquire, so that predictive models can be designed to simulate and optimize fluid dynamics for CO2 injection and storage applications.

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