Abstract

Central Sumatra is presently the principal oil producing area of Indonesia. The vast basinal area of Central Sumatra was formed during the Early Tertiary. Conveniently three areas of Tertiary sedimentation may be recognized : the West Coast Islands, the Intramontane Basins and the Central Sumatra Basin.

Central Sumatra Basin tectonics are characterized by horst and graben structures and transcurrent faulting. There are two dominant fault trends : one, northerly or parallel to the Malaysian structural trend; and the younger northwesterly trend parallel to the Semangko fault. Paleogene and Neogene sediments are present in the Central Sumatra Basin. The Paleogene paralic and non marine clastics filled and are preserved in Pretertiary grabens. Neogene sediments represent an older transgressive phase during the deposition of the Sihapas and Telisa lithologic units, and a younger regressive phase, during the deposition of the Petani Formation. The stratigraphy of the West Coast Islands and Intramontane Basins can be correlated to that of the Central Sumatra Basin.

Early Miocene paleogeology in Central Sumatra Basin is characterized by a dominantly deep marine basinal shelf facies to the west, that laterally interfingers with a shallower sand/shale shelf facies to the east and northeast. The Sihapas Group is the shallower lateral time equivalent of the basinal Telisa shales. The two rock units form a genetic sequence and are the source-reservoir system for hydrocarbon generation and accumulation.