Awang H. Satyana*
The opening mechanism and nature of the basement underlying the North Makassar Straits has been debated for almost thirty years. Two leading opening mechanisms are: tectonic escape through major strike-slip extension and back-arc rifting due to subduction rollback. The basement has been debated as continental or oceanic. This study presents hard data of the North Makassar Straits’ basement penetrated by two exploration wells: Rangkong-1 (ExxonMobil Surumana, 2009) and Kaluku-1 (ConocoPhillips Kuma, 2011). The basement’s analyses include: petrography, X-ray diffraction, biostratigraphy, petrochemistry, magnetic susceptibility, multi-isotope geochronology, and organic geochemistry. Oils discovered by Kaluku-1 well in Eocene section provides further information based on analyses of bulk properties, carbon isotope, and various biomarkers. These hard data, never published anywhere before, are the basis for this study. The new data constraint that the basement of the Makassar Straits is Gondwanan Paternoster-West Sulawesi microcontinent, thinned due to rifting from the Early/Middle Eocene to Early Miocene time as response to back-arc rifting related to subduction roll back in SE Sundaland. The Eocene rifted grabens and horsts were the sites for shallow lacustrine sources, sandstone reservoirs, and traps. Kaluku oil discovery show the active petroleum system in West Sulawesi Offshore. Based on Kaluku discovery, further exploration should target the area to the east of Kaluku until transition zone with Onshore Sulawesi. Here the source rocks are considered to be thicker, better quality, earlier maturation hence generating more oils. The sandstone reservoirs will also be thicker. Syn-rift play may also be significant here, but existing seismic data preclude the evaluation. New 2D high resolution or 3D seismic data are required for better evaluation. Dry wells drilled here by various operators from 2009-2012 did not condemn the area since none of these wells targeted the Eocene section on rifted structures that actually should be.
Proceedings, Indonesian Petroleum Association, Thirty-Ninth Annual Convention and Exhibition, May 2015, IPA15-G-104.
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