## 3 Results
### OM Characterization by Rock-Eval Pyrolysis  
The OM properties of the target samples (rock specimen taken from the same depth within a well section) are characterized by the Rock-Eval technique (Table 5). According to S2 values, samples 1/2 and 13/15 show extremely high generation potential. TOC content varies in the range of 5.39-16.98 wt.%. According to the pyrolytic parameters, the maturity of Oil field 1 and Oil field 2 is at the beginning of the oil window. Oil field 3 parameters correspond to the peak of oil generation. All specimens of the initial samples were prepared using a single-point drilling scheme. The same applied to most samples after combustion resulted in core fragility. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Sample ID**} & \multirow{2}{*}{**Oil Field**} & **S1** & **S2** & **S3** & **TOC** & **Tmax** \\ \cline{3-6}  & & **mg HC/g Rock** & **mg HC/g Rock** & **mg CO2/g Rock** & **wt.\%** & \({}^{\circ}\)C** \\ \hline
1/2 & 1 & 3.96 & 100.2 & 0.34 & 14.01 & 424 \\
10 & 1 & 1.41 & 36.65 & 0.39 & 6.01 & 429 \\
12 & 1 & 0.63 & 38.36 & 0.24 & 5.39 & 428 \\
13/15 & 2 & 6.30 & 107.6 & 0.2 & 16.98 & 433 \\
16/18 & 3 & 6.95 & 31.26 & 0.31 & 7.98 & 446 \\ \hline Avg. & & 3.85 & 62.81 & 0.29 & 10.07 & n/a \\ SD & & 2.83 & 37.69 & 0.08 & 5.15 & n/a \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Pyrolytic properties of samples before CT.  
Figure 11: Change in the fluid saturation by NMR after the combustion. To better understand the effect of the combustion front on a larger scale (than that used for sand or core pack), we decided to perform 2D pyrolysis on three samples after the CT experiment. The core plugs were selected from different sections of the tube: #12 (Figure 12b) and #15 (Figure 12c) from the highest temperature zone 4, #10 (Figure 12a)--from the lowest temperature zone 6. Heat maps, showing distributions of free hydrocarbons, as the sum of peaks S0 and S1 in classic pyrolysis, kerogen (S2 in classic pyrolysis), and TOC values for three samples are shown in Figure 12, correspondingly. Samples #10 and #12 were initially characterized by similar values of non-transformed kerogen according to the S2 parameter (Table 5). Figure 12a shows that sample #10 from the low-temperature zone (6.1, 207 \({}^{\circ}\)C) has a relatively uniform transformation of organic matter in its volume. The opposite type of distribution of non-transformed kerogen (S2) is observed in sample #12 from high-temperature zone 4.1, 463 \({}^{\circ}\)C (Figure 12b). The zones A1, C4, D4, E:1-4 of sample #12 (S2) exhibit a higher transformation degree than in other analyzed points, which can be explained by an initial uneven distribution of OM or the impact of void structure (for example, fractures occurred) on the OM transformation process during combustion. Overall, sample #12 (Figure 12b) shows the full conversion of kerogen, which is confirmed by the low content of free hydrocarbons. It proves that a temperature of 463 \({}^{\circ}\)C is sufficient for the near-complete conversion of the organic matter in the consolidated core samples. This confirms that the combustion front has passed through the entire rock sample. From the distributions of free hydrocarbons (S0 + S1), also more uniform distribution is shown in the volume of sample #10 comparing with sample #12. Therefore, sample #15 was exposed to a lower temperature (422 \({}^{\circ}\)C) than that for sample #12, and might store a liquid oil phase that was not removed from the combustion tube. Sample #15 (Figure 12c) also comes from the high-temperature CT section, but it shows significant residual saturation. First of all, a certain amount of kerogen remains in the sample. Figure 12: Distributions of S0+S1 (evaporated hydrocarbons content, mg HC/g rock), S2 (HC products of kerogen decomposition content, mg HC/g rock), and TOC (%wt.) after thermal exposure in samples (a) #10; (b) #12. (c) #15. A second, relatively high value for S0 + S1 and TOC indicates the presence of liquid free oil.