Publications

Despite being originally part of one of the first ever PSCs awarded in Indonesia back in 1967 the Biliton basin still represents today one of the countrys last remaining unexplored frontiers. The basin is one of a series of Tertiary basins (Palembang, Sunda, North Seribu Trough, Asri, Arjuna, Zaitun, Vera, etc.) located on the southeast margin of the Sunda craton that originated during a major Eocene-Oligocene period of extension and later Miocene sag. Overall the depression forming the basin covers an area in excess of 12,000 km2 and contains within it two, north-south oriented, Palaeogene rift depocentres. Seismic data indicates more than two seconds of sedimentary section representing a likely depth to basement in excess of 4000 m (>13,000 feet). In between these two rift trends is a largely platformal area characterized by the presence of a series of very large (~ 30 km), west-east trending basement highs which exhibit a characteristic “inversion appearance. These structures appear to largely pre-date the Mid- Miocene unconformity which is often seen to truncate the uplift throughout the Biliton area.The basin fill ranges in age from ?Eocene to the Holocene and exhibits syn-rift deposits passing upwards into post-rift sag and later transgressive sediments. As is the case in the nearby Arjuna basin, two syn-rift sequences characterize the early rift fill. Syn-rift I (?Eocene) which lies unconformably on basement is interpreted to be equivalent to the Jatibarang (Java) or Lahat (Sumatra) Formations. Syn-rift II (Oligocene) which lies with angular discordance either above syn-rift I or the basement is interpreted to be equivalent to the Lower Talang Akar (Java) or Banuwati (Sumatra) Formations. By analogy to basins nearby, both syn-rift sequences are thought to contain intervals of non-marine source rocks which in the case of the syn-rift II sequence have a characteristic low frequency reflection characteristic on seismic data.In the Sunda, Asri and Arjuna basins commercial fields are located either within the rifts themselves or within 30 km of the rift kitchens. There is limited long distance migration and hydrocarbons are trapped in a variety of settings in the syn-rift, thermal sag or post rift related clastic/carbonate reservoirs. In some basins structural trapping appears dominant (e.g., Arjuna, Sunda) whereas in others, stratigraphic traps are where the majority of the reserves can be found (e.g., Asri). Current mapping in the Biliton basin has identified a series of trap types on a variety of different stratigraphic levels with reserves potential far in excess of a billion barrels.While at the present time it cannot be proven without doubt that a functioning petroleum system exists in the Biliton basin, there is no doubt that all the ingredients necessary for its development are present and the recently acquired seismic data confirms that burial of potential source rock intervals should have resulted in a hydrocarbon (oil) charge. Furthermore, the results of the earlier seabed coring studies conducted in the basin by BP in the early 1990s perhaps should now be taken more seriously. The algal oil recovered in these seabed cores confirms the view that some type of mature lacustrine source rock exists in the rift depocentres. The lengthy migration path from the kitchen to the site of the seeps (± 30 km) would suggest, although by no means prove, that a reasonable charge exists in the basin and further exploration is warranted.