Publications

Oil on the Island of Seram, eastern Indonesia, was first observed as numerous seeps on the coastal plain of the east coast and this led to the discovery of the Bula Field in 18- 97. Since its initial exploitation in 1913, over 14 million barrels of oil have been produced from both the shallow Pleistocene carbonate and clastic reservoirs, together with the underlying Late Triassic and Early Jurassic carbonate and nearshore clastic sediments.The hydrocarbons range from heavy naphthenic crudes to lighter, more paraffinic, condensate-like oils. Despite this variation which is attributed largely to biodegradation, the biomarker characteristics of the oils are both distinctive and remarkably uniform over the entire eastern Seram area, irrespective of field occurrence, reservoir age or lithology. The distinctive combination of geoche_mical fossils observed is unique amongst the oils of South Easth Asia, although a natural bitumen fromButon Island (South East Sulawesi) bears many similarities.To date, the origin of the Seram oils has proved enigmatic, as have the geology and tectonics of the associated sediments. Various source rocks have been suggested including the Plio-Pleistocene sequence, a Miocene carbonate section and the Triassic-to-Jurassic sediment.Recent geochemical data published on oils and source rocks from both central Australia and central America defined some biomarker patterns similar to those of the Seram oils. These published studies demonstrated that the oils were sourced from carbonates in either evaporite or marine micritic sequences. On the basis of these associations, it is concluded that the biomarker character of the Seram oils is a reflection of a very specialised carbonate depositional environment.This conclusion seemed to implicate a distinctive dark Late Triassic micritic limestone as a possible source of the Seram oils. While subsequent analysis failed to support this, the presence of the micritic carbonate does demonstrate that similar specialised carbonate environments exist in the area. The geochemically inferred depositional environment of such a carbonate unit is consistent with its position within the tectonic setting and evolution of the Banda Arc region.Such an oil to source to tectonic relationship has regional geological significance in that dark micrites are present on other islands of the Banda Arc (Timor and Buru) and on Buton. The shallow Bula Field in Seram and some of the light oil seepages on Timor and Buton may be evidence of oil accumulations at depth sourced from this apparently widely distributed distinctive carbonate unit. Not all the oils of the region, however, are related to these distinctive source units.