Petrographic features of oil-prone coals from the Brunei-Muara District, Negara Brunei Darussalam

Abstract

Petrological investigation of a number of coal samples from the Brunei-Muara District reveals the presence of oil-generative features commonly observed in oil-prone coals. These features include the occurrence of exsudatinite, oil globules, oil haze and changes in fluorescence intensity; all of which were observed to be associated with the maceral suberinite and bitumens in the samples studied. These liptinitic constituents, which are commonly associated with liptodetrinite, are regarded as the most oil-prone components in the coals of the Brunei-Muara District. Exsudatinite is developed by fracturing of the vitrinite following generation of fluid hydrocarbons. This leads to expulsion of hydrocarbons under sufficient pressure to cause the fractures to develop and form exsudatinite crack network. This occurs at a relatively low thermal maturity level of 0.42 to 0.49%R o ' These coals are characterised by a high abundance of liptodetrinite, inertodetrinite and vitrodetrinite occurring within a desmocollinite (or collodetrinite) matrix, and occasional mineral matter. The presence of a high ab undance of hydrogen-rich liptodetrinite and its association with collodetrinite further enhances the oil-generative and expulsive features possessed by these coals. In these coals, liptodetrinite seems to be mostly derived from the breakdown of the suberinite-phlobaphinite framework , primarily by fragmentation of suberinite. This breakdown is associated with liquid hydrocarbon generation. The generation of liquid hydrocarbons by the liptodetrinite maceral, however, was not observed at this low thermal maturity and is likely to occur later at a relatively higher maturation level.