Abstract

Geochemical analyses of Oligocene to Pliocene samples from the Sunda Basin, offshore Southeast Sumatra, indicate that source rocks are present in the Oligocene Talang Akar and in the lower Miocene Batu Raja Formations. Shales rich in amorphous and herbaceous kerogen, with TOC values ranging from 1.0 to 6.0%, are present in the middle and lower sections of the Talang Akar Formation. The upper Talang Akar section, mostly a coaly unit, contains shales with up to 38.0% TOC, in which woody and coaly material predominate. Pyrolysis and extract analyses indicate that the coals have good source rock potential. The overlying Batu Raja Formation exhibits TOC values of up to 3.0%, and is also dominated by woody and coaly organic matter.

Vitrinite reflectance and pyrolysis analyses indicate large oil generative areas in four depocenters of the Sunda Basin.

Eight oil families were identified. Chromatographic and isotopic characterization of oils and source rock extracts, indicate generation from both terrestrial and aquatic kerogen types. Crude oil to source rock correlations suggest that oils produced from the center or along the western margin of the Sunda Basin were generated mostly from middle Talang Akar source rocks, and that oils accumulated along the eastern margin of the Sunda Basin were derived mostly from the lower Talang Akar section.

Maturation modelling shows that oil generation from lower Talang Akar source rocks commenced in middle late Miocene time, indicating that late generation and migration prevailed in the Sunda Bain. Hydrocarbon migration followed both stratigraphic and fault pathways.