Publications

Middle Miocene Balikpapan Group coals from a well-exposed section near Samarinda, Kalimantan, have been analysed by petrography, bulk geochemistry and quantitative pyrolysis-gas chromatography to investigate peat biomass and early diagenetic controls on oil generation from coaly rocks of the Mahakam Delta. Coals from a deltaic-shallow marine interval have high total and organic sulphur contents (Stot 1.74 -8.07%, Sorg 1.20 -3.67%), relatively high hydrogen contents (HI 208 -288 mg HC/g TOC) and lower Tmax values (401 -412°C) than coals from an overlying fluvial interval (Stot 0.28 -0.52%, Sorg 0.26 -0.48%, HI 173 -211 mg HC/g TOC, Tmax 414 -422°C). This suggests the likelihood of earlier generation and more efficient expulsion of oil from coaly rocks within the more marine-influenced sequences. All of the analysed coals are humic, with high vitrinite (73 -92 vol.%) and low to moderate inertinite (1 -18%) and liptinite (6 -16%) contents. Two identified endmember coaly organofacies are interpreted as planar and raised mire facies. Pyrolysate n-alkyl group compositions predict the analysed coals to have potential to expel petroleum compositions ranging from borderline gas condensate to high-wax, paraffinic-naphthenic-aromatic crude oil. Nonvolatile (nC15+) paraffinic oil yields are low -moderate (4.2 -12.9 mg/g TOC), but more extensive sampling is likely to reveal some greater potentials for high-wax, paraffinic oil. The non-volatile, paraffinic oil potential of Mahakam Delta coals appears to be controlled primarily by the abundance of the leaf- and cork-derived cutinite, suberinite and liptodetrinite macerals. These macerals are expected to be overall more abundant in thin, planar mire coals and associated coaly mudstones than in generally thicker, raised mire coals owing to the better preservation potential of surface leaf biomass under generally higher groundwater levels in planar mires. Further investigations are planned to confirm this.