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Stratigraphic And Structural Pattern In Onshore Bengkulu Basin. Case Study: Implication To Hydrocarbon Play In Indonesia Frontier Area


Bengkulu Fore-arc basin covers both offshore and onshore areas in the western part of Southern Sumatra. It is located between the magmatic-volcanic, inner arc of the Barisan Mountains and the non-volcanic, outer arc ridge of the Mentawai Islands. The stratigraphy of the onshore Bengkulu Basin consists of a series of Oligo-Miocene up to Pliocene sediments overlaying unconformably the pre-Tertiary basement complex. Bengkulu basin is a complex basin with stratigraphy and structural pattern that allows the presence of petroleum system. The TOC values of the Oligo-Miocene Seblat Fm as source rocks range from 0.5-2.0%, the hydrogen index varies from 150-380, while T-max values are in the range of 433-457. The main reservoir targets are basalt transgressive sandstone and limestone of Oligo-Miocene Seblat Fm and regressive limestone of Mid-Miocene Lemau Fm. Hydrocarbon could be trapped in reefal, stratigraphic, faults, and anticlines and sealed by Middle-Late Miocene claystones and siltstones of Simpang Aur Formation. Low geothermal gradients due to the forearc's position over a subducting lithospheric plate are one of the factors in the lack of discovered oil. Another problem is the fault bounded the basement high to the east to act as a sealing fault so the migration of hydrocarbon from the adjacent sediment-filled graben would have been blocked. This preliminary study uses geological maps and basin evolution to know how the stratigraphy and structural patterns have been formed in Bengkulu Basin. Recent regional gravity data shows that the onshore part of Bengkulu Basin is composed two major N-S oriented structural grabens. Through all data analyses can be interpreted how stratigraphic and structural pattern development, assessment, and its implication to hydrocarbon play in Bengkulu Basin.

Keyword: Bengkulu Basin, Hydrocarbon, Stratigraphy, Structural Pattern.