Abstract

Source rocks in the hydrocarbon productive basins in Indonesia can be classified as lacustrine, fluvio-deltaic and marine. Lacustrine source rocks are the most productive, and have sourced most of the oil in Central Sumatra, some of the oil in the Sunda Basin and also possibly oil in the West Natuna Basin. Fluvial-deltaic source rocks are the most common and widely dispersed and have sourced oil in the majority of foreland (back-arc) basins of Western Indonesia. Marine source rocks probably occur in Eastern Indonesia, but are poorly documented. However, they may have sourced oil in the Salawati Basin and eastern Sulawesi. Positively identified producing source rocks are all Tertiary in age, although Pre-Tertiary (Permian/Jurassic) rocks are suspected to source oil in the Bintuni and Bula (Seram) Basins and are also a possible source in eastern Sulawesi and the Banggai-Sula area east of Sulawesi.

Crude oils in Indonesia can also be characterized as lacustrine, fluvio-deltaic and marine based on a range of geochemical parameters, including pyrolysis-gas chromatography on the oils asphaltene fraction and GC-MS biomarker data. Lacustrine oils sourced from non-marine algae are generally low-medium gravity, waxy, low sulfur oils and often contain unusually high concentrations of C30 4-methyl steranes. Marine oils derived from marine algae are low-medium gravity, low wax, medium-high sulfur oils and contain C27-C29 diasteranes and steranes in relatively high concentrations compared to other oil types. Fluvio-deltaic oils derived from higher plant, terrestrial organic matter are medium-high gravity, waxy, low sulfur oils. They contain abundant higher plant resin derived C30 alkanes and low concentrations of steranes which are dominated by C29 diasteranes and steranes.