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Tectonics, Structures, and Implication for Petroleum Systems: Cases from Indonesia October 30, 2011

Posted by ugmsc in Course and Workshop Summary.

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This course aims to give a view of the typical petroleum systems found in Indonesia. Petroleum system is a natural system that encompasses a pod of active source rock and all related oil and gas and which includes all the geologic elements and porcesses that are essential if a hydrocarbon accumulation is to exist. The essesntial elements include: a petroleum source rock, reservoir rock, seal rock, and overburden rock. The processes are trap formation, the generation-migration-accumulation of petroleum, and preservation of accumulation.

Seen from tectonics point of view, Indonesia is rich with tectonic diversities. Hamilton (1979) states that Indonesia represents an ideal level of complexity for analysis  within the framework of available concepts of plate tectonics.

According to their position within a plate, basins are classified into several categories: intracratonic sag basin, terrestrial rift basin, passive continental margin, oceanic basin, foreland basin, backarc basin, forearc basin, trench, and strike slip basin. On an active basin, basins available are backarc and  forearc basin. In total, there are 86 tertiary basins of Indonesia of 128 basins in total.

Western Indonesia is a microcontinents collage, with primary tpe of rifted and inverted basin. It mainly consists of Sunda platform, with also north Sumatera basin, Central Sumatera basin, South Sumatera basin, Sunda Basin, West Natuna Basin, etc. for Sundalan basin, middle to late Eocene timing for initian basin rifting and associated fluvio-lacustrine fill, including the main source rocks. Transgression from middle Oligocene through to the middle Miocene with fluvial reservoirs being succeeded by the main deltaic and carbonate reservoir in the late Oligocene to early Miocene, and regional seals being deposited in the middle Miocene at maximum transgression. Late Miocene through Pliocene compressional structuring events and increased heat flow associated with the collision of Australian Craton and collision of the Luzon arc with the Asian Plate.

For the Makassar schematics of Play, the primary play is reservoir of oligocene – miosen carbonate buildups on tilted fault-blocks, source of Eocene coals with potential lacustrine facies in grabens, seal of deepwater Oligocene-Miocene shales.

For petroleum from areas with gliding tectonics, it is mainly of the deformation by gravity sliding-gliding tectonics. Kutai Basin of Samarinda Anticlinorium. The volcanic centres are mainly Miocene and associated with the gold deposits. The same mechanisms of gravity sliding-gliding tectonics is also true in North Serayu Basin, Central Java.

Whereas petroleum system from collisional terranes is found in Southeast Kalimantan, Central Sulawesi, and mostly at Eastern Indonesia. Collision occurs across a converging  plate margin when two masses that are too light to sink meet a subduction zone. The boundary between the two masses is called a suture zone. The ideal anatomy of collisional orogen consists of foreland basin, forelad fold/thrust belt, suture, internal metamorphic/igneous zone, and retro fold/thrust belt. The prominen example is the drifting and collision history of Banggai-Sula micro-continent.

The last petroleum system is the system from Australian passive margin. This type is found for most of the basin in Papua, which is Southern Banca Arc-Arafura Shelf-NW Australian Shelf.



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