## 4 Discussion  
For geological CO\({}_{2}\) storage (GCS), possible CO\({}_{2}\) leakage pathways impact three risk category areas: containment, site performance, and public perception [48]. Therefore, it \begin{table}
\begin{tabular}{l l l l} \hline  & & **Original** & **120 h** & **240 h** \\ \hline BET Surface Area (m\({}^{2}\)/g) & & 14.5298 & 15.1392 & 15.4480 \\ Total Volume in Pores (cm\({}^{3}\)/g) & \(\leq\)1.066 nm & 0.00233 & 0.00259 & 0.00287 \\ Area in Pores (m\({}^{2}\)/g) & \(>\)1.066 nm & 8.953 & 8.769 & 8.787 \\ Total Area in Pores (m\({}^{2}\)/g) & \(\geq\)0.367 nm & 16.758 & 17.176 & 18.363 \\ \hline \end{tabular}
\end{table} 
Table 4: CO\({}_{2}\) adsorption summarized report. Figure 7: CO\({}_{2}\) adsorption isotherms of the pre- and post-test samples. is important to understand the effects of mineralogical variability and heterogeneity on the geochemical response of the geological storage system to the injection of CO\({}_{2}\). The results of previous studies conclude that different mineralogical compositions significantly influence the patterns of geochemical and geophysical reactions, and hence the geological properties of CO\({}_{2}\) due to injection [14; 49; 50; 51]. Since the main confining properties of the sealing rock are closely related to the content of the clayey material, it is crucial to understand the reactivity of these minerals in interaction with scCO\({}_{2}\) in wet conditions to assess the performance and safety of the geological storage system. Few studies have shown relevant experimental results and modelling models for illitization phenomena under CO\({}_{2}\) storage conditions for clay rocks [52; 53]. This work explores these implications in common carbonate-rich clay such as marl, called blue marl, as well as assesses impacts on the sealing capacity of cap rock. The first result of this study carried out under conditions close to those found in CO\({}_{2}\) geological storage systems, evidenced a process of illitization of smectite and mixed-layer illite-smectite that gradually transforms into illite under acidic conditions (carbonic acid). The illitization process of the smectite layers was observed by XRD. The illitization process of the smectite layers was observed by XRD. The illitization process could be due to the dissolution/decomposition of the smectite layers that release Al\({}^{3+}\), Mg\({}^{2+}\) and Fe\({}^{2+/3+}\) ions from the octahedral sheets, as shown by the ICP-EOS results. The decrease in the K content would be in opposition to the illite precipitation. An important implication of the integrity of clayey seal rock caused by the illitization process of mixed-layer illite-smectite is the increase in porosity due to the alteration of the structures of the smectite layer [52; 53], which is classically associated with a decrease in particle volume and loss of water molecules. Structurally, the smectite layers reduce their size in the basal direction, from 12-15 A to the size of the illite (10 A) by loss of hydration and change of exchange cations in the interlayer. A significant volume of illitization could result in the formation of microcracks that could interconnect over time and cause the undesirable leakage of gas from the confining region to materialize. CO\({}_{2}\) injected into a moist environment promotes the generation of carbonic acid and bicarbonate anions in solution, reducing the pH to between 3-5 [22; 25; 54]. Reduced pH causes the weathering of aluminosilicates in the rock, such as smectites. It also causes the dissolution of carbonate minerals, such as calcite in the marl studied. The dissolution of primary minerals and the consequent contribution of cations (Fe\({}^{2+/3+}\), Ca\({}^{2+}\), Mg\({}^{2+}\), Na\({}^{+}\), and Al\({}^{3+}\)) buffer the pH and can achieve alkaline solution values (around 7-8) [24].