## 4 Results
### Mass Balance Calculation and Numerical Modelling  
The mass balance calculation indicates dissolution of calcite, dolomite, quartz and pyrite and precipitation of illite and gypsum. The total amount of dissolved and precipitated minerals as well as the final mineral composition is presented in Table 4.  
The mass balance has been done assuming that changes of Mg concentration in the fluid are due to dolomite dissolution only and no Mg-rich mineral precipitated. The mass of dissolved pyrite is calculated using the Fe concentration and the gypsum amount is evaluated by sulphate concentration changes after the pyrite calculation. Quartz dissolution is calculated using the Si concentration changes  
Figure 4: Changes in the pore network configuration of the limestone after SC CO\({}_{2}\) rich brine exposure. (**a**) Before (left) and after (right) images obtained by OpM showing an increased connectivity between pores after the experiment; (**b**) Before (left) and after (right) images obtained by SEM showing an increased surface roughness of calcite crystals due to dissolution at three different scales. while the amount of illite is evaluated using the amount of K concentration. No precipitations of other clay minerals such as kaolinite are considered here, even if in other recent studies kaolinite precipitation has been considered the most favourable secondary alteration mineral [49; 50; 51]. Here, we stipulate that without alumino-silicate in the initial rock sample such as albite or microcline, kaolinite precipitation is not expected. Moreover, illite is initially identified in the rock sample composition which can accelerate the nucleation step. Regarding the results of the numerical modelling, we can observe in Table 4 that the simulated results are similar to those obtained by the mass balance calculation. The main reaction is calcite dissolution even if the saturation index for calcite was not as low as for dolomite (Figure 5). This difference is explained by the calcite dissolution rate (kinetics and reactive surface area). Illite precipitation is also predicted by the model as calculated from the mass balance. Actually, the saturation index for illite remains quite high at the end of the simulation indicated that equilibrium is not yet reached and more illite precipitation may occur. In the simulation results, we can observe that calcite and gypsum have reached equilibrium at the end of the experiment, while dolomite is still under-saturated with respect to the fluid. The secondary minerals that were finally used in the calculations are given in Table 4 and are in agreement with the ones supposed for the mass balance calculation. The kinetics data presented in Table 4 and used in this study are in agreement with other studies performed in similar temperature and pressure conditions [27; 43; 50; 51; 52]. methodology. This is in agreement with the preliminary expectations based on theoretical models and results of similar experiments [3; 20; 24]. The absence of available pore water precludes the development of a low pH environment and the consequent carbonate dissolution; while other processes possibly provoked by dry CO\({}_{2}\) injection, such as drying of clay minerals or particle movement, were not expected in this case due to the high carbonate content of the rock and the static nature of the experimental setup. Dry or almost dry conditions are possible to evolve in near-well situations where the injected CO\({}_{2}\) displaces most of the pore water and the high CO\({}_{2}\)-brine ratio results in the dissolution of the remaining (e.g., capillary) water [7]. Under these conditions the chemical reactions are not really relevant and any changes induced in the pore configuration will be due to other processes. On the other hand, with increasing distance from the injection point, the amount of pore water increases [7] and the chemical reactivity of the system becomes a dominant factor. Our experiment modelling water saturated conditions produced obvious chemical and physical changes in the reservoir rock.