CO2 injection into saline aquifers as part of the CCS process induces chemical processes represented with CO2 dissolution into water and minerals reactions which can disturb the brine equilibrium and changes the aquifer’s petrophysical properties. This thesis aimed for implementing numerical tools for assessing the interactions between carbon dioxide, the original brine, and the aquifer minerals with more focus on exploring the parameters that could optimize the amount of solubility and mineral trapping. The study was done on Dogger carbonate aquifer in Paris Basin. Modelling was done with PHREEQC and CMG-GEM. PHREEQC was used for assessing geochemical reactions of injecting a fixed partial pressure CO2 into the aquifer with the objective of assessing the effect of pressure, temperature, the pH, the solution’s ions, and mineralogy on geochemical trapping. It was split into two parts aimed for studying each of the mechanisms separately. CMG-GEM was used for 2D reactive transport simulations for studying the effect of physical and chemical trapping mechanisms in addition to assessing this software compatibility with PHREEQC. The main results showed that the abundance of sodium in the solution relative to calcium and magnesium could help increase CO2 solubility and the system pH. For minerals reactions, trials were done to simplify the system with equilibrium modelling and applying partial equilibrium into kinetic simulations which showed that silicate minerals reaction rates would be overestimated with semi-kinetic modelling. For the base case, mineral trapping was mainly from albite dissolution to form dawsonite, while other carbonate minerals contributed less. As part of sensitivity analysis, higher pressures and temperatures were found to be helpful for increasing mineral trapping but it is the pressure that affect the speed of dawsonite precipitation. By testing minerals effect, albite was found to lead to more mineral trapping with higher volume fractions, while illite led to the opposite even though both are silicate minerals. With higher calcite volume in the system, minerals’ reaction rates could be slowed down leading to achieve lower porosity reduction and better equilibrium pH, but lower mineral trapping. Primary carbonate minerals were essential for achieving a positive mineral trapping from the beginning. On the other hand, minerals were found to have no effect on solubility trapping. Ramping up the complexity with reactive transport simulation showed that geochemistry modelling of GEM is compatible with PHREEQC results. Moreover, mineral trapping was found to be minimal with around 1% contribution to trapping after one thousand years. The main result of RTM suggested that carbonate precipitation is faster with CO2-rich brine compared to supercritical CO2. In conclusion, this thesis showed that carbonate formations could be advantageous for better pH buffering and less effect on the aquifer storage in addition to that existence of certain cations-holding minerals could ramp up the mineral trapping significantly