## 4 Results
### Petrographic and Chemical Characterization of Carbonate Rocks after SC CO\({}_{2}\) Injection
#### 4.2.2 Sc Co\({}_{2}\) Rich-Brine  
The composition of the brine was analysed using a combination of techniques before the experiment (Table 2 \"Pure Brine\" column). The brine that was used in the experiment was recovered immediately after the end of the test for a comparative chemical analysis. The results are given in Table 2 (\"Brine post-test\" column). The comparative analysis revealed chemical changes that surpass the uncertainty range of the applied methods. The Mg\({}^{2+}\), Ca\({}^{2+}\), HCO\({}_{3}\)\({}^{-}\), NO\({}_{3}\)\({}^{-}\), SiO\({}_{2}\) and conductivity values increased significantly, while the pH decreased. The rest of the analysed parameters (Na\({}^{+}\), K\({}^{+}\), SO\({}_{4}\)\({}^{2-}\), Cl\({}^{-}\), CO\({}_{3}\)) do not present significant alterations.  
The optical observations carried out by OpM and SEM (Figure 4) demonstrate obvious changes in the calcite mineral grains as compared to the natural sample. In particular, dissolution textures can be observed including (i) the apparition of secondary pores on the surface of calcite minerals and (ii) a relatively rough surface after CO\({}_{2}\)-brine-rock interaction (Figure 4b). Quantification of the optical pore parameters by OIA revealed an increase in number of pores (12.26%) and in total pore area (4.12% to 4.44%) due to the formation of new pores and the increase in size of the existing ones. Pore morphology was also affected as shown by the increased aspect ratio and the decrease in the roundness parameter (Table 3). The XRF analysis however did not reveal significant changes in the whole rock composition after the experiment (Table 1 \"Rock after CO\({}_{2}\) and brine\" column).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Component** & **Pure Brine (mg/L)** & **Brine Post Test (mg/L)** & **Interpretation** \\ \hline Na\({}^{+}\) & 982 \(\pm\) 98.2 & 1000 \(\pm\) 100 & No change \\ K\({}^{+}\) & 94 \(\pm\) 9.4 & 92 \(\pm\) 9.2 & No change \\ Mg\({}^{2+}\) & 84 \(\pm\) 8.4 & 106 \(\pm\) 10.6 & Increase (26\%). Dissolution of Dolomite \\ Ca\({}^{2+}\) & 266 \(\pm\) 26.6 & 1040 \(\pm\) 104 & Increase (290\%). Dissolution of Calcite \\ SO\({}_{4}\)\({}^{2-}\) & 223 \(\pm\) 22.3 & 240 \(\pm\) 24 & No change \\ Cl\({}^{-}\) & 2180 \(\pm\) 218 & 2180 \(\pm\) 218 & No change \\ HCO\({}^{-}\)\({}_{3}\) & 17 \(\pm\) 1.7 & 2400 \(\pm\) 240 & Increase (1400\%) \\ CO\({}_{3}\) & 0 & 0 & No change \\ NO\({}^{-}\)\({}_{3}\) & 1 \(\pm\) 0.1 & 7 \(\pm\) 0.7 & Increase (600\%) \\ SiO\({}_{2}\) & 13 \(\pm\) 1.3 & 17 \(\pm\) 1.7 & Increase (31\%) \\ pH & 7.4 (pH) & 6.4 (pH) & Decrease (13\%) \\ \hline Conductivity & 6450 (mS/cm) & 13650 (mS/cm) & Increase (112\%) \\ \hline \hline \end{tabular}
\end{table}
Table 2: Chemical analysis of pure brine and brine taken from the reaction chambers. Uncertainty (10%) given by IGME Laboratory.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Number of Pores** & **\(\Delta\) Number of Pores** & **Porosity (\%)** & **A Porosity** & **Ro** & **\(\Delta\)Ro** & **As** & **\(\Delta\)As** \\ \hline Before & 11.17 \(\times\) 10\({}^{4}\) & 12.26 & 4.12 \(\pm\) 0.15 ** & 7.77 (0.32) * & 0.625 & \multirow{2}{*}{\(-\)2.40} & 2.07 & \multirow{2}{*}{\(-\)2.26} \\ After & 12.54 \(\times\) 10\({}^{4}\) & 12.26 & 4.44 \(\pm\) 0.17 ** & 7.77 (0.32) * & 0.610 & & 2.257 & \multirow{2}{*}{\(-\)2.26} \\ \cline{6-6}