## 4 Hydrocarbon Potential of formations in Malaysia
### Organic Geochemical Characteristics of Formations in Peninsula Malaysia (PM)
#### 4.1.2 Source Quality  
Rock-Eval pyrolysis is the most reliable analytical technique to provide information about kerogen type [19; 69; 86]. The analyzed dataset from the Rock-Eval allows the derivation of HI and OL, which is equivalent to the H/C atomic ratio and O/C atomic ratio, respectively [69; 79; 86]. The average OI values of the Belata, Semanggol, Kroh, Semantan, and Batu Arang formations ranged from 2.03 to 31.50 mgCO\({}_{2}\)/g, and their average HI values ranges from 0.02 to 347.38 mg HC/g (Table 3). The Belata and Kroh formations had very low HI and OI values, making it difficult to get a good reading from the plot in Figure 5. There were indications that the samples in both the Semantan and Semanggol formations were of type IV kerogen (Figure 5). However, according to [PERSON] [17] the Semantan and Semanggol formations appear gas-prone because type IV kerogen is basically inert and does not really influence S2, but contributes to the TOC, which lowers the HI. The similarities in the kerogen type of both the Semantan and Semanggol formations could be associated with part of both formations being formed in the Triassic period.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**No.** & **Formation** & **Avg TOC (wt\%)** & **Interpretation after [PERSON] [79]** & **Reference(s)** \\ \hline
**1** & Belata & 3.32 & Very good & [8] \\ \hline
**2** & Semanggol & 2.85 & Very good & [13; 14; 52] \\ \hline
**3** & Kroh & 2.21 & Very good & [53] \\ \hline
**4** & Semantan & 2.68 & Very good & [13; 52] \\ \hline
**5** & Batu Arang & 41.23 & Very good & [54; 55] \\ \hline
**6** & Penyu & 15.84 & Very good & [56] \\ \hline
**7** & Batu Gajah & 1.33 & Good & [57] \\ \hline \end{tabular}
\end{table}
Table 2: Interpretation of average TOC values of formations in Peninsular Malaysia according to [PERSON] [79].  
Figure 4: A plot of average S2 versus average TOC of formations in Peninsular Malaysia showing hydrocarbon yield potential and type of kerogen.  
To evaluate the kerogen type of the Batu Arang formation and Penyu basin, Tmax and HI values were used, due to limitations on the availability of OI data for those formations in the open literature. The average Tmax of the Batu Arang formation and Penyu basin was 416.86 \({}^{\circ}\)C and 416.35 \({}^{\circ}\)C, respectively, and the average HI was 463.43 and 434.80, respectively (Table 4). The Batu Arang formation and Penyu basin have type II and type I kerogen types, respectively (Figure 6). This shows that the organic matter from the Penyu basin originated from algal material deposited in lacustrine environments, thereby producing mostly waxy oil [17]. The Batu Arang having type II organic matter gives the impression that it originated from autochthonous organic matter deposited under reducing conditions in marine environments. As a result, it primarily produces naphthenic oil [17].  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**No.** & **Formation** & **Av Tmax (\({}^{\circ}\)C)** & **Av HI (mg HC/g)** & **Reference(s)** \\ \hline
**1** & Batu Arang & 416.86 & 463.43 & [54] \\ \hline
**2** & Penyu & 416.35 & 434.80 & [56] \\ \hline \hline \end{tabular}
\end{table}
Table 4: Average Tmax and HI values of Batu Arang and Penyu formations in PM.  
Figure 5: OI vs. HI plot showing the type of kerogen of formations in PM.  
The classification by [PERSON] [79] (Table 5), that uses the HI vs. S2/S3, suggests that the Belata and Kroh formations are type III, which indicates that they generate gas. Furthermore, the organic matter from the Belata and Kroh formations is derived from terrestrial plant debris or aquatic organic matter deposited in an oxidizing environment, and, thus, might mainly produce gas [72]. The Semantan and Semanggol formations were also classified according to [PERSON] [79] classification and indicated type III kerogen, and this confirmed the conclusion that type IV kerogen appears to be gaseous.