Publications

The island of Buton which is located on the southeastern arm of Sulawesi, is famous for its surface deposits of asphalt. Some people may consider that the manifestation of asphalt is indicative of a sealing failure, but from the analysis of tectonic, stratigraphic and geochemical aspects, there still exist the possibility for oil accumulations.The tectonic setting of Buton shows that Buton is at the site of a double collision. The first collision occurred between the Muna and Buton microcontinents in the Miocene. Analogous to the Muna collision, Buton also collided with the Tukang Besi micro-continent from the east side in the Plio- Pleistocene times. This collision caused uplift which exposed the potential oil source rocks and reservoir formation of the Buton micro-continent.Those tectonic activities have affected the stratigraphy across the Buton Basin. The southern part of Buton experienced more uplift as compared to the northern part. This uplift resulted in exposure of hydrocarbon source rocks and reservoir which made them vulnerable to biodegradation from meteoric water flushing, especially since the source rock type is classified as kerogen Type II. The reservoir and source rock formations are considered at the flank of an elongate culmination in the centre of Buton Island with almost north-south trending.Geochemical data from shallow drilling (Tobing, 2005) in the Sampolawa area, Buton, indicates the thermal maturity of the rocks to be immature with the vitrinite reflectance ranging from 0.2-0.6%. However, oil seeps occur not only in drilled cores but also from surface outcrops which indicate the expulsion of hydrocarbons. Hence, maturation has taken place at certain depth and condition where the heat flow is more intense.The possibility of hydrocarbon accumulation is also considered to be in the eastern offshore Buton. The W-E seismic sketch of eastern offshore Buton shows that the land sediments are still continuous to the eastern slope of Buton. Based on biodegradation model proposed by Satyana and Wahyudin (2000), it is expected that the reservoir and source rock which sank to the western and eastern part of the culmination was protected from meteoric water flushing and any oil contained has not biodegraded yet.By reviewing work and publications about Buton, this paper is to stimulate the idea that oil exploration in Buton is not over yet. The offshore Buton is considered prospective where the reservoir and source rocks are still buried at depth.