ISPG Webinar #15 Petroleum Geology of North Sumatra Basin

The North Sumatra Basin is a part of the Greater North Sumatra Basinal area, located in the northwestern corner of Indonesia, considered a the back-arc basin the the West Sunda Island Arc system. The Great North Sumatra Basinal area includes the Andaman Basin, with oceanic crust formed by as a back-rifting, the Mergui Basin, the Paseh Basin, while the North Sumatra Basin are almost an appendage-like extension of the basinal area toward the southwest. The whole basinal area is known to be underlain by continental crust. To the east the basinal area is bordered by the Sundaland, while to the west it is bordered by the Bukit Barisan Range, volcanic arc built upon an uplift exposing Pre-Tertiary and Paleogene sediments. Offshore to the North the Bukit Barisan Range suddenly narrows down to a row of volcanic islands, the Andaman Islands, The fore-arc basin, which is well developed west of the Bukit Barisan Range also narrows down to vanish being incorporated in the accretionary ridge of the West Sunda Subduction zone.
The tectono-stratigraphy of North Sumatra basin is typical of the West Indonesia basins, with the exception of the presence of Pre-Rift Paleocene sedimentation consiting of the Tampur
Formation forming a carbonate platform overlying the Pre-Tertiary basement which toward the western part of the Bukit Barisan Range has developed into the Meureudu Volcanics. Syn-Rift deposition took place on the Tampur platform, depositing the Bruksah Fm and Bampo Fm with marine influence, in north-south trending grabens. The Post-Rift sequence consist of the Early Miocene carbonate Peutu Fm with reef build-ups, and clastic Belumai Fm. The Peutu Fm appears to extend over the present day Bukit Barisan Range developing clastic members, indicating that the Bukit Barisan Volcanic Arc did not exist yet at this time. This is followed by the deposition of the deep marine Baong Fm, as the North Sumatra Basn began to be down-warped as the back-arc basin began to develop and the Bukit Barisan Range was uplifted in Middle Miocene time. As the Bukit Barisan emerged above sea-level, sedimentary provenance switches from the Sundaland in the east to the uplifted Bukit Barisan in the west, and Syn -Oorogenic megasequence depositing the regressive clastics of the Late Miocene -Pliocene Keutapang Fm, Seurula Fm and Julurayeu Fm , followed by the coarse clastics of the Idi Fm in Pleistocene time.
The tectonics of the North Sumatra Basin is dominated by the NW-SE shearing movements of the basement, due to the stress of the oblique subduction of the island arc system. which caused inversions of the graben bounding basement faults developed during the Paleogene. This shearing movement are responsible for the development of folding of the Neogene strata, forming the anticlines, which are not consistently trending NW-SE as one would expect if a NE directed compressive stress is assumed.
North Sumatra Basin is known to contain oil and gas resources since the 19th Century, as a matter of fact the first oil field discovered in Indonesia, Telaga Said field, is located in the southeastern part of this basin, while the Arun Gas Field the first giant gas field in Indonesia is also located in this basin.
The source rock is believed to be mainly in the syn-rift Bampo Fm, while reservoirs are provided mainly by the reefs of the Peutu Fm, and the sandstones of the Keutapang Fm, the latter in anticlinal traps. Minor fields have also been discovered in transgressive Belumai Fm, and in the turbidite sands of the Baong Fm.