A Comparison Study of West and East Natuna Basin, Indonesia: Tectonic-sedimentary Evolution and Hydrocarbon Distribution

The West and East Natuna Basin are typical intracratonic rifted basins within the Sunda Shelf of Southeast Asia. The two, which are geographically adjacent and separated by a N-S trending basement high in the Natuna Sea, the... [ view full abstract ]

The West and East Natuna Basin are typical intracratonic rifted basins within the Sunda Shelf of Southeast Asia. The two, which are geographically adjacent and separated by a N-S trending basement high in the Natuna Sea, the Natuna Arch, have a very different evolutionary and sedimentary history due to the shelter from the Natuna Arch. Development of both basins began during Late Eocene to Early Oligocene time where extension phase was pervasive and responsible for formation of half grabens filled with nonmarine sediments throughout the whole area, but the rift magnitude in the East was generally less than the one in the West Natuna Basin. Subsequently, the two were in the post-rift thermal subsidence phase resulting in the formation of the first regressive/transgressive cycle. Compressional stress began to dominate in the West Natuna Basin from Early Miocene time, producing uplift and inversion of the former structural pattern. Simultaneously, the East Natuna Basin remained tectonically quiescent and was still in the post-lift subsidence phase. During Middle Miocene time, it happened slight inversion giving rise to intermittent faulting, uplift, localised erosion and subaerial exposure in the East Natuna Basin. By Late Middle Miocene time, tectonically quiescence and stable conditions prevailed again and have persisted in the West and East Natuna Basin until the present day, deposited in predominantly marine environments. The comparison of regional geological setting and hydrocarbon accumulation conditions reveals contrasting characteristics of hydrocarbon distribution in these two basins. In the West Natuna Basin which experienced intensive structural deformations, hydrocarbon is mainly enriched in Upper Oligocene-Lower Miocene fluvio-deltaic to fluvial and alluvial sandstones, while in the East Natuna Basin where tectonically quiescence was common, hydrocarbon is mainly enriched in Middle Miocene-Lower Pliocene platform and reefal carbonate build-ups. The ultimate recoverable reserves in the East are obviously more than the ones in the West Natuna Basin, especially gas reserves. Future exploration targets in both basins exist in clastic sequences of the deep formation with low exploration level in common, draping structural and stratigraphic-unconformity plays around the permeter of the West Natuna Basin and untested reefal carbonate build-ups in the East Natuna Basin.