Publications

Tertiary basins encircling Sundaland (circum-Sundaland Basins) of Western Indonesia (North Sumatra, Central Sumatra, South Sumatra, Sunda-Asri, West Java, East Java, Barito, Kutei, West Natuna, East Natuna, South Makassar, West-South Sulawesi Basins) were formed in the Mid-Eocene to Early Oligocene. The basins were formed mostly as tectonic responses due to collision of India to Eurasia, they were formed by: (1) trans-tensional rifting induced by regional post-collision tectonic escape or (2) back arc rifting induced by roll-back movement due to slower rate of Eocene subduction. Thick intervals of Paleogene sediments were deposited in early, middle, and late phases of rifting, as well as early phase of post-rifting of the basins, covering depositional environments ranging from nonmarine, lacustrine, fluvio-deltaic, paralic, marginal- to shallow marine facies. These sediments are important hydrocarbon source rocks in the basins. Few wells or no well penetrated these sources, causing precise interpretation of the source facies is impossible due to the absence of samples for biostratigraphic analyses. However, interpretation of the source facies can be assessed by detailed examination of biomarkers of oils generated from these sources (geochemical inversion). Varied biomarkers are encountered, revealing the variability of their source facies. Characteristic of oils generated are various caused by their various source facies, but the facies variability of each basin is typical and predictable, systematically expressing its tectonic and sedimentary settings on and around the Sundaland. Sedimentary basins around the Sundaland show roughly similar tectonostratigraphic history during the Paleogene and Neogene, basically including histories related to: pre-rifting, syn-rifting, post-rifting, sagging, and syn-inversion. Differences of these basins lay on the time initiation of each tectonostratigraphic unit and its sedimentary facies. The latter is determined by the position of the basin relative to the Sundaland. These sedimentary basins (North Sumatra, Central Sumatra, South Sumatra, Sunda-Asri, West Java, East Java, Barito, and West Natuna) produce oils from Paleogene and Neogene reservoirs, but the oils were generated from Paleogene source rocks. Basins of South Makassar and West-South Sulawesi also have generated oils from their Paleogene sources as proved by testing of well/s or seeps. Kutei Basin produces oil generated from Neogene deltaic sources, whereas its Paleogene source is not proven yet generated oil due to these rocks are very deeply buried by stacks of Neogene deltaic sediments. The facies variability of these Paleogene sources is best examined by biostratigraphic analysis of the rocks. However, these rocks are located within the kitchen of each basin and almost no well penetrate the kitchen. Therefore, the examination is based on oils generated from these sources through oil geochemistry analyses. A number of oil biomarkers are ample tool to reveal the source facies of oils.