## 4 Hydrocarbon Potential of formations in Malaysia
### Organic Geochemical Characteristics of Formations in Peninsula Malaysia (PM)
#### 4.1.3 Thermal Maturity  
Vitrinite Reflectance (R\({}_{\rm o}\)) is the principal thermal maturity indicator in hydrocarbon exploration [76, 87]. However, not all the formations had vitrinite reflectance analysis done according to the data analyzed. As a result, R\({}_{\rm o}\) was calculated for the formations without R\({}_{\rm o}\) data, using the Duvernay shale model [R\({}_{\rm o}\) = (0.0149 \(\times\) Tmax) \(-\) 5.85] [68]. The range of R\({}_{\rm o}\) values of the formations in Peninsula Malaysia was 0.39% to 3.58%, with an average value of 1.38% (Table 6). The Belata Formation had the highest R\({}_{\rm o}\), with the Penyu and Batu Arang Formations having the lowest values of 0.39 and 0.41, respectively (Table 6). According to the standard interpretations of the stages of organic matter maturity by [PERSON] [88], the samples from Batu Arang and Penyu were immature (Table 6). The immature nature of the Batu Arang and the Penyu indicated that the organic matter in these formations had not been exposed to deep burial and thermal cracking to generate hydrocarbons. It also indicated that the samples from Semantan and Semanggol formations were in the late oil generation stage. Finally, the interpretation by [PERSON] [88] suggests that the Belata formation samples had generated dry gas, while that of Kroh had also generated wet gas. Tmax vs. PI plots are often used to determine the maturity, and they provided results similar to those obtained from the interpretation based on [PERSON] [88] classification. According to the Tmax vs. PI plots, the samples from Batu Arang and Penyu were immature, while  
Figure 6: Tmax vs. HI plot showing the type of kerogen in PM.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Formation**} & \multirow{2}{*}{**Av S2/S3**} & **Av HI (mg** & **[PERSON] [79] Source** & \multirow{2}{*}{**Reference(s)**} \\  & & & **HC/g)** & & **Quality Interpretation** & \\ \hline
**1** & Belata & 0 & 0.02 & Gas & [8] \\ \hline
**2** & Semanggol & 0.36 & 22.89 & Gas & [13,14] \\ \hline
**3** & Kroh & 0.06 & 1.42 & Gas & [53] \\ \hline
**4** & Semantan & 1.06 & 26.18 & Gas & [13,52] \\ \hline \hline \end{tabular}
\end{table}
Table 5: Source quality interpretation of formations in PM using [PERSON] [79] interpretation.  
the samples from Semantan and Semanggool were in-between the oil and gas zones. The Belata and Kroh formations had matured to the dry gas stage (Figure 7). According to the HI vs. Tmax plots, the Batu Arang, Kroh, Belata formations, and Penyu basin were in the pre-oil stage, indicating that they were still immature (Figure 8). However, the HI vs. Tmax plots results for the Belata and Kroh formations differed from the R\({}_{\text{o}}\) and Tmax vs. PI plots. This could have been because of the relatively low HI resulting from the low S2 values. Generally, Tmax values of rocks with very low S2 values (<0.2 mg HC/g rock) can be inaccurate [79; 89]. The Semantan and Semanggool formations were in the wet gas/condensate zone indicating higher thermal maturity than the others.