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Tectonic Evolution and Hydrocarbon Potential in the Fore-arc Basins of Western Indonesia

Abstract

The fore-arc region of western Indonesia is extended for more than 3000 km in length from Sumatra to Java Islands. It can be divided into four different areas based on bathymetry and geology. These are North Sumatra, West Sumatra, Sunda Strait and Southern East Java. This paper will discuss comparison and hydrocarbon potential based on newly acquired 2D seismic data and the current knowledge of regional tectonic supported by fieldworks. Based on current tectonic model, it shows that the western Indonesia fore-arc region was formed during Late Eocene and continues to the present time. The sediments within the fore-arc basin are mostly very thick consisting of shale, sandstone and limestone deposited in various depositional setting including deltas, shallow marine, slope and deep marine turbidities. It was very clear evidence from wells and seismic data that this region was developed as fore-arc since Early Miocene. The basement composition is considered as important parameters in determining the prospectivities of the region. Most of the areas are interpreted underlain by transitional crust consisting of previous subduction mélanges and older fore-arc sediments except for North Sumatra and Southern East Java which are show possibilities of continental crust. In addition, deformation in the fore-arc region is relatively low except for Sunda area which shows several evidence of series young normal faulting related to the Sumatra Fault zone. This model will definitely affect the interpretation of hydrocarbon prospectivities of the region in negative way in particular related to the present of source rocks and their maturity since traditionally fore-arc region is considered having low gradient geothermal. In summary, our study indicate low to moderate hydrocarbon potential of the Western Indonesian Fore-arc region due to several parameters including: limited data showing evidence of petroleum system occurrences, uncertainty in tectonic and depositional model, hydrocarbon maturity and migration and deep water setting considering as very high risk or consider as frontier area. However, in Early to Middle Miocene large reef complexes was recognized and mapped which can act as major reservoir rocks for this region. Potential hydrocarbon could be generated in the basin, therefore large accumulation will be expected particularly for North and west Sumatra fore-arc areas.