Carbon capture and storage is key for sustainable economic growth. CO₂-enhanced oil recovery (EOR) methods are efficient practices to reduce emissions while increasing oil production. Although it has been successfully implemented in carbonate reservoirs, its effect on wettability and multiphase flow is still a matter of research. This work investigates the wettability alteration by carbonated water injection (CWI) on a coquina carbonate rock analogue of a Pre-salt reservoir, and its consequences in the flow of oil. The rock was characterized by routine petrophysical analysis and nuclear magnetic resonance. Moreover, micro-computed tomography was used to reconstruct the pore volume, capturing the dominant flow structure. Furthermore, wettability was assessed by contact angle measurement (before and after CWI) at reservoir conditions. Finally, pore-scale simulations were performed using the pore network modelling technique. The results showed that CWI altered the wettability of the carbonate rock from neutral to water-wet. In addition, the simulated relative permeability curves presented a shift in the crossover and imbibition endpoint values, indicating an increased flow capacity of oil after CWI. These results suggest that the wettability alteration mechanism contributes to enhancing the production of oil by CWI in this system.

Total dissolved solids (TDS) is an important property in the characterization of natural waters for diversified applications, such as in geochemistry and the petroleum industry. Under appropriate circumstances, the determination of this parameter through correlations with the electrical conductivity (EC) of aqueous systems yields considerable advantages over the gravimetric method. However, the development of empirical equations correlating TDS and EC is still required due to the physical-chemical complexity of charge transport in multicomponent natural waters. Most existing correlations were built considering systems in the lower or medium salinity range. In this context, this research aims to provide experimental correlations between TDS and EC in a broad concentration range for high salinity formation brines characteristic of the pre-salt reservoirs. It contributes to filling a gap in the literature for geochemical systems of this nature. Moreover, correlations were also obtained for a concentrated desulphated seawater and an aqueous sodium chloride solution in the same salinity range. For all aqueous solutions, the polynomial fittings of degree greater than one fit the experimental data better compared to both linear and exponential equations. In addition, the solutions with higher concentration of divalent ions had lower EC than the solutions dominated by monovalent ions with the same ionic strength. This evidences the effect of ion pairing on the EC, particularly in solutions of high ionic strength. Therefore, the use of a general correlation to represent solutions with dramatic variations in chemical composition carries substantial error, particularly in the high salinity range. Thus, a specific correlation must be developed to represent brines with similar composition.

Brazilian Pre-Salt carbonate reservoirs are natural candidates for Enhanced Oil Recovery combined with Carbon Capture and Storage due to their high CO₂ production. However, the effect of CO₂ on rock wettability still needs to be investigated to build representative reservoir models to predict the ultimate oil recovery. This work applied contact angle measurements to study the consequences of carbonated brine on the initial wettability. Moreover, coreflooding experiments were carried out to evaluate the incremental oil recovery obtained by carbonated brine injection. Finally, nonreactive tracer tests and micro computed tomography were used to observe the effects of mineral dissolution on the sweeping efficiency. Carbonated brine induced a decreased oil-wet behavior caused by rock dissolution and desorption of organic compounds resulting in a contact angle reduction of 55° for the Pre-Salt rock. This contributed to obtain a 27% increase in oil recovery. Moreover, tracer tests and micro computed tomography verified the formation of preferential flow paths by mineral dissolution. The increased oil production and decreased contact angle encourage further studies on the injection of carbonated brine for the Pre-Salt scenario.