NEW INSIGHTS INTO THE PETROLEUM GEOLOGY OF THE MOUNTAIN FRONT AREA CENTRAL SUMATRA BASIN

摘要

Geographically the mountain front area as defined in this paper is located on the southern margin of the Central Sumatra Basin (CSB). The area is elongate to the southeast-northwest parallel to Barisan Mountain and is bordered by Tigapuluh Mountain in the southeast and the Asahan Arch in the northwest. The petroleum potential and maturity of the mountain front area has not been proven especially when compared with the northern coastal plains area of the CSB. Very extensive exposures of Pre-Tertiary to Neogene outcrops and the complex structural history of the area cause difficulties in assessing its hydrocarbon potential. A series of dry holes and non-economic hydrocarbon well results suggests the need for a new strategy in petroleum exploration, slightly or even completely different to that implemented in the northern area. Updated surface geological mapping and petroleum system information will certainly change the old petroleum system concepts. The area's petroleum evolution began during the Eocene to Oligocene with a trans-tensional rift event which deposited lacustrine and fluvial facies. The coal and siliciclastic lithologies of the facies are potential source and reservoir rocks, respectively. Subsequently, in latest Late Oligocene to Middle Miocene, deposition gradually changed to transitional and then marine facies as post-rift sediments. The latest deposits are considered a regional seal. The presence of volcanic materials and immature clastic sediments indicate that the provenance is relatively close to the basinal area. Structural traps formed since the Middle Miocene due to compression which culminated with the peak of the Barisan uplift in the Plio-Pleistocene. This event reactivated and rejuvenated pre-existing older basement structures. The synthesis and conclusions of this paper which is based on outcrop observation integrated with subsurface data, now need to be tested and validated with drilling results.