--> Manui Basin's Petroleum System Elements: Insight From Surface Geological Observation for Frontier Hydrocarbon Exploration in Indonesia

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Manui Basin's Petroleum System Elements: Insight From Surface Geological Observation for Frontier Hydrocarbon Exploration in Indonesia

Abstract

Manui Basin is a frontier basin in the south-east arm of Sulawesi, adjacent to Buton and Salabangka Basin. The island was formed by collision between drifted part of southeastern Sundaland and drifted micro-continents of the Indian-Australian Plate (Satyana et al., 2011), resulted in various lithology. Even though there has been no discovery, some evidence such as asphalt outcrop within Jurassic Tokala shale and gas seepage in Upper Meluhu and Tokala mix-siliciclastic sedimentary rock from the similar age were found in the field, indicating active petroleum system. Field observation including measured stratigraphy, geological structure measurements, and rock sampling was accomplished in this study. The result is expected to be analogue and support subsurface analysis later. In Manui Basin, deposition started in Upper Triassic to Middle Jurassic, producing calcareous sedimentary rocks succeeding to metamorphic along with the rifting phase. The formations consist of Pompangeo and Mekongga Fm. (schist and gneiss), Meluhu Fm. (sandstone succeeding to meta-sandstone or phyllite), Tokala & Laonti Fm. (meta-limestone, calcareous oil shale, marble). Deposition was absent until Matano Fm. (calcilutite with shale intercalations) was formed between Lower Cretaceous and Lower Paleocene. Ophiolite was formed around Middle Eocene before Salodik Fm. which shows succession of sandstone and limestone as product of inversion phase. The last are molasse sequence deposited in Middle Miocene to Holocene. The sequence consists of Langkowala, Pandua, Boapinang, Eemoiko, Alangga Fm., and uplifted corals. Beside claystone of Meluhu Fm., asphalt among outcrops of Tokala Fm. makes the formation an upcoming candidate for source rock. Lithologies with suitable properties as reservoir candidate can be found among sandstone in upper Meluhu and Langkowala. Sandstones of upper Meluhu are composed of well-sorted wacky sandstones with rounded grains and dominated by quartz, while Langkowala's are poorly sorted gravelly sandstone with subangular grains and dominated by lithic fragments. Meluhu's carbonaceous shale and Tokala's calcareous shale are considered as cap rock due to their fine grains (low permeability) and low quartz composition resulting in a less brittle characteristic, while clay and marls from Boepinang are less qualified due to their quartz abundance. Last but not least, stratigraphic trap (inter-fingering sandstone and shale of Meluhu and Tokala) is expected in study area.