PALEOGEOGRAPHY RECONSTRUCTION OF PEMATANG GROUP IN NORTH AMAN TROUGH, CENTRAL SUMATRA BASIN
Central Sumatra Basin is a proven prolific basin. Most of hydrocarbon accumulation are in post-rift interval of Sihapas Group, meanwhile the syn-rift interval of Pematang Group is still under-explored. Nevertheless, there are remaining risk and uncertainty of reservoir geometry and distribution in this interval. The previous study on Pematang Group were not utilizing 3D seismic with integration with well data to identify sandstone reservoir distribution in North Aman Trough. Paleogeography reconstruction of Pematang Group with integration of well and seismic data as in this study will be useful to reduce risk and increase chance to find new resources.
Approximately 1,230 sq. km of 3D merged post-migrated seismic cube which were tied to 45 wells in North Aman Trough have been interpreted with tectonostratigraphic approach. Main structure on this area is a series of Northwest – Southeast normal fault that was developed during Eo-Oligocene. Those faults were inverted to thrust fault during Middle Miocene – recent. Paleogeography reconstruction were inferred from conventional core data, wireline log electro-facies, seismic geomorphology, isopach map as proxy of paleo-topography and rift tectonostratigraphy model.
Biostratigraphy data suggests gradually changing on Eocene-Oligocene paleoenvironment from terrestrial to marine transition. However, foraminifera fossil had just occurred in Early Miocene as indication of marine incursion. Core data indicates lithofacies of sand flaser and mud lenticular which is associated to rapid changes of sedimentation flow due to rainfall rate or climate.
Paleogeography of Pematang Group is influenced by three rift tectonic stages: 1) rift initiation, with environment of alluvial plain, alluvial fan and fluvial meander; 2) rift climax, with environment of deep lacustrine, shallow lacustrine, marginal lacustrine, nearshore lacustrine, deltaic, fluvial meander, alluvial plain and fan delta; 3) immediate post-rift, with environment of fluvial braided and alluvial plain.
Key words: paleogeography, tectonostratigraphy, rift