Aliphatic hydrocarbon distribution as fingerprint for reconstructing the paleoenvironment of the Miocene coal from Muara Teweh Mine, Warukin Formation, Barito Basin, Kalimantan

Low-to medium-rank coal reservoirs are considered to have the potential to store biogenic gas reserves and can be processed through downstream thermochemical gasification to produce synthetic gas. To prove this, biomarker analysis of four coal samples collected from the Muara Teweh Mine, Warukin Formation, Barito Basin, Kalimantan, was performed to investigate the organic geochemical characteristics and provide information regarding the viability of coal as a biogenic gas reservoir. The determination of aliphatic hydrocarbon distribution using Gas Chromatography-Mass Spectrometry (GC-MS) shows groups of 22 n-alkanes, 2 isoprenoids, 20 hopanoids, and 5 bicyclic sesquiterpenoids. The n-alkane biomarkers with unimodal distribution and the prevalence of long-chain over short-chain carbons, particularly at n-C₂₉, indicate the source of organic matter is dominated by terrigenous plants with low maturity and high biodegradation rates. This is also strengthened by the distribution of hopanoids and the presence of unstable compounds such as 17β(H)-22,29,30-trisnorhopane (βTm) and 4,4,8,9,9-pentamethyldecalin. Very high ratios of Pr/Ph (15.26–22.36) and the ratios of C₃₂/C₃₁ hopane and C₂₉ αβ/C₃₀ αβ indicate a hyperoxic environment for deposition. The crossplot results show that the coal samples involved are humic coal and classified as type Ⅲ kerogen, which is gas-prone. The overall results of the biomarker analysis indicate that the studied coals can be transformed into gas form through gasification, as evidenced by the degree of biodegradation and maturity.