## 4 Discussion
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample ID**} & \multicolumn{4}{c}{**Before CT**} & \multicolumn{4}{c}{**After CT**} \\ \cline{2-9}  & \multirow{2}{*}{**Total Fluid Volume (cc)**} & **Bitumen \&** **Structural \&** & **Modified** & **Total Fluid** & **Bitumen \&** & **Structural \&** & **Robified Oil** \\  & & **MoMolecule Oil (\%)** & **Molecule Oil (\%)** & **Molecule Oil (\%)** & **Molecule Oil (\%)** & **Molecule Oil (\%)** & **Molecule Oil (\%)** & **Molecule Oil (\%)** & **Molecule Oil (\%)** \\ \hline
1 & 0.42 & 84.22 & 8.40 & 5.34 & 0.33 & 86.45 & 8.13 & 5.96 \\
2 & 0.34 & 86.29 & 6.45 & 6.72 & 0.17 & 68.66 & 26.75 & 5.26 \\
3 & 0.32 & 82.14 & 7.65 & 8.16 & 0.002 & 31.72 & 13.10 & 18.62 \\
10 & - & - & - & - & 0.49 & 28.78 & 64.39 & 7.19 \\
12 & - & - & - & - & 0.28 & 44.74 & 41.67 & 10.53 \\
14 & 1.14 & 93.83 & 2.53 & 2.02 & 8.10\({}^{\circ}\)* & n/a & n/a & n/a \\
15 & 0.76 & 77.68 & 16.19 & 11.23 & 0.32 & 81.20 & 2.87 & 14.36 \\
16 & 0.86 & 59.98 & 42.18 & 4.54 & 0.03 & 88.84 & 7.77 & 5.18 \\
18 & 0.90 & 59.25 & 41.09 & 5.12 & 0.72 & 0 & 20.83 & 0 \\ \hline Avg. & 0.68 & 77.63 & 17.78 & 6.16 & 0.29 & 53.45 & 23.19 & 8.39 \\ SD & 0.32 & 13.23 & 16.80 & 2.93 & 0.24 & 31.98 & 20.83 & 5.89 \\ \hline \hline \end{tabular}
* the total fluid volume of the sample is too small for component separation.  
\end{table} 
Table 7: Results of NMR T\({}_{1}\)–T\({}_{2}\) interpretation for target samples before and after CT.  
Figure 13: Pore size distribution for target samples (a) #2, CT section; (b) #12, CT section  
It is noted that the most intensive organic matter transformation was in the middle of the sample. NMR analysis also confirmed the absence of a liquid phase in sample #12 and confirmed its presence in samples #1, 2, 10, and 15. In this work, we attempted to define the correlations between parameters obtained, such as gas porosity and permeability, residual saturation by NMR, S2 value, and exposed temperature (Figure 14). Notably, for all samples, we observed an increase in porosity and permeability. A crossplot for gas porosity relative change (Figure 14a) shows that there is a good correlation between porosity and the section temperature. In the case of NMR saturation of the rock (Figure 14b), we observed a direct relation of change in NMR fluid volume and CT zone temperature. At higher temperatures in CT, more HC fluid in the rock is displaced, resulting in lower residual saturation by NMR. When plotted for gas permeability (Figure 14c), it is less pronounced and can be applied for mainly 3-4 samples (in the 400-470 \({}^{\circ}\)C range). This also applies to the S2 value change (Figure 14d), which directly indicates the kerogen transformation in rock. Decreased S2 values prove the generation of synthetic oil during the combustion process. In turn, NMR and Rock-Eval results demonstrate the presence of liquid oil, which remains in rock samples and therefore, is not collected at the tube fluid samplers. For this reason, the TOC content should not be considered as an OM indicator within the combustion experiment. However, samples exposed to the same temperature demonstrate different behavior. This confirms the presence of multiple factors influencing the change in rock properties. Besides the CT section temperature, other important factors include the rock lithology, OM content, and maturity. Thus, the exposure temperature, location in the combustion tube (section), and initial properties of the rock might significantly affect the combustion results. In our case, we investigated samples from three oil fields with different rock lithology and OM maturation (Table 3). Oil fields 1 and 3 are of similar rock lithology--siliceous organic-rich shales. Oil field 2 is represented by mixed argillaceous-siliceous rocks. In turn, all oil fields have various OM maturity--oil fields 1 and 2 are at the beginning of the oil window but with higher generation potential for oil field 2.