## 3 Results  
To determine the transformation due to the interaction of scCO\({}_{2}\) with clay minerals in the sealing rock, the oriented aggregates prepared from the fine fraction were glycolate by solvation with ethylene glycol (EG) solvation and were subsequently examined by XRD (Figure 3). The composition of clay minerals and their evolution with scCO\({}_{2}\) tests and the labelling of the initial spacing positions d\({}_{001}\) of smectite (Sm), illite (I), and kaolinite (Ka) (d\({}_{001}\)\(\sim\) 17, 10 and 7.1 A or 20 \(\sim\) 5.1\({}^{\circ}\), 8.8\({}^{\circ}\) and 12.4\({}^{\circ}\), respectively), were included for better understanding. For illite and kaolinite, the X-ray patterns or intensity reflections were the same, with no significant variations. However, smectite and mixed-layer illite-smectite showed a decrease in intensity in the treated samples of the original. In more detail (Figure 4), it was observed that after 120 h of reaction, the reflection d\({}_{003}\) at 5.9 A corresponding to the smectite practically collapsed. Likewise, the CO\({}_{2}\) interaction corresponds to the (70%) illite/(30%) smectite interstratified (002/003) with spacing close to 5.2 A. The illitization reaction was also confirmed by a significant sharpening of the 5.0 A peak ((004) illite). However, a new peak appears, identified as the reflection (002/003) of the interstratified illite/smectite with 40% illite [38; 39]. In addition, a decrease in intensity and a shift in the low-angle peak corresponding to 001 of the smectite to lower spacing can  
Figure 3: Comparison of XRD patterns of original blue marl oriented and original ethylene-glycol blue marl, after 120 and 240 h of interaction with sc-CO\({}_{2}\) (highlighted, see Figure 4). be observed. The shift of the gravity peak of glycol gravity-peak shift from 17.1 A (5.15\({}^{\circ}\)20) to 16.5 A (5.32\({}^{\circ}\)20), is more characteristic of a mixed-layer I/Sm (glycol) (Figure 3). At 240 h, a positive strengthening in the intensity of the reflection corresponding to the interstratified (40% illite) was observed, as well as a slight increase in intensity and a significant sharpening (higher symmetric peak) for the reflection of 004 of the illite (d\({}_{004}\) - 5.0 A). This slight increase in the intensity of the illite (Figure 3) was also observed for reflection 006 (d\({}_{003}\) - 3.3 A). A possible dissolution and illitization process of the original smectite and mixed-layer was observed. The original mixed-layer with 70% illitic layers developed to 100% illitic layers (completed illitization) after 120 h. However, part of the original smectite began the illitization resulting in a new mixed layer (with around 40% illitic layers). A (semi) quantitative analysis of the mineral phases present and their evolution with supercritical CO\({}_{2}\) treatments was performed by Rietveld refinement. Table 1 (Figures S1-S3 in the Supplementary Material) shows the (semi) quantitation results of the original (original blue marl) and treated common clay after 120 h and 240 h. A decrease in the smectite and interstratified content was observed, due to possible dissolution in acid medium (pH 3.3-3.5, estimated by [PERSON] et al. [41]). On the contrary, an increase in illite content was observed, along with an increase in carbonate mineral phases, calcite (CaCO\({}_{3}\)), dolomite (CaMg(CO\({}_{3}\))\({}_{2}\)), and siderite (FeO\({}_{3}\)); the siderite is not present in the original sample. These results would agree with the fact that smectite in the treated samples was destroyed by dissolution, as well as the destruction or illitization of smectite in interstratified illite/smectite to illite. Additionally, a proportion of cations released in the dissolution/destruction of the mineral phases involved precipitate in the carbonate phases, chemically fixing CO\({}_{2}\). The precipitation of siderite (iron carbonate) was not significant.