Abstract Coals are known to be source rocks for natural gas, but also for liquid petroleum. Laboratory experiments under controlled physical and chemical conditions can help to understand maturation and hydrocarbon generation in these rocks. Whole-rock cuboids of two bituminous coal samples (0.60% and 0.80% vitrinite reflectance) were subjected to semi-closed hydrous pyrolysis under isothermal conditions for 24 h at 300, 310, 320, 330, and 340 °C. This study aims to investigate the alterations of coal in terms of microscopic observations and organic geochemical data. Significant alterations in liptinite and vitrinite were observed at 320 °C: megasporinite and sporinite partially transform into bitumen, with oil droplets filling newly formed porosity and bubble-like voids appearing within vitrinite bodies. At 340°C, most liptinite is converted leaving behind voids interconnected by cracks. Inertinite, however, remains apparently unchanged after the experiments. Temperature of maximum pyrolysis yield and vitrinite reflectance increase systematically with experimental temperatures, while the Hydrogen and Oxygen Index values determined by Rock–Eval pyrolysis tend to decrease, though with some variations. This decrease is attributed to the loss of oxygen, present e.g. in hydroxyl and carboxyl groups within the coal, as well as the loss of aliphatic and aromatic hydrocarbons resulting in the decrease in H/C and O/C ratios. These reactions and an increase of the relative abundance of short-chained n - and isoalkanes with increasing HP temperatures basically follow the trends observed during natural maturation.
Arysanto et al. (Sat,) studied this question.