The Central Sumatra Basin is part of a back arc basin located on the southwest edge of the Sunda Shelf. This basin represents the largest oil-producing basin in Indonesia. Petroleum system in Central Sumatera Basin showed that Sihapas Formation is good reservoir, and most explorationists concern and continue to search for oil and gas reserve in this formation. Based on our research, however, we still have another good quality reservoir in Central Sumatera Basin, which is the Pematang Formation. This research aims to reveal the sedimentology and petrography characteristic of Pematang facies from surface outcrops in Rantauberangin and surrounding area, Riau Province. The analysis includes verticallateral distribution of reservoir rock, stratigraphic columns correlation of measured sections and reservoir quality consisting of megascopic and microscopic (thin section petrography) analyses. The typical and character of the five Pematang facies were identified on the study area; i.e.: braided channel facies, oxbow lake – meandering channel facies, paleosol – braided river facies, gravity flow (low energy) facies, and debris flow – alluvial fan (high energy) facies. The braided channel facies have good reservoir quality and debris flow facies have poor reservoir quality. Overall, paleogeography of the study area during Pematang time suggesting a semi-enclosed continental valleys bounded by normal fault creating alluvial fan, some of which poured into deep lakes and in the other end of the valley braided and meandering rivers might have also occupying the area.
Author : Warto Utomo, Dwi Hendro H N, Kristian Simanjuntak, Andi Krisyunianto, Andang Bachtiar