Publications

The Pematang-Sihapas(!) petroleum sq stem of Central Sumatra is one of the most important lacustrine oil systems in Southeast Asia The Brown Shale Formation (lacustrine) of the Pematang Group has generated ~60 x 109 barrels of oil Sihapas (Early Miocene) sandstones are the principal reservoirs of this system Giant fields (eg., Minas and Duri) having Sihapas (marine sandstone) resen'oirs occnr principally along the eastern margins of sub-basins Smaller fields having Pematang (nonmarine sandstone) resenoirs are confined to the deeper troughs.The Pematang Group was deposited in a series of small grabens It exhibits a tripartite stratal architecture basal (Lower Red Bed) fluvial/alluvial unit, medial (Brown Shale) lacustrine unit. and upper (Upper Red Bed) fluvial/alluvial unit The Upper Red Bed unit is the main Pematang reservoir Source rock attributes of the Brown Shale are highly ~ariable Pyrolysis yields of samples containing > 1.0 wt.% TOG range up to ~120 mg HC/g rock. with a mean of -25 3 ing HC/g rock The oil-proneness of the kerogen also varies The more oil-prone portions of the unit appear in the upper portion of the stratigraphic unit and in the fully lacustrine facies (i.e., poor source rock dcveloprnent occurred in lake margin, deltaic and fan delta facies) Geochemical differences also exist among the di ff crent sub-basins.The Peinatang Group is disconformably overlain by the Menggala Formation (basal transgressive unit of Sihapas Group) Mcnggala strata consist of wellsorted quartzose to subarkosic sandstones having an average norosity or > 20% and an average permeability of 1500 md Menggala sandstones are the most prolific hydrocarbon reservoirs in Central Sumatra.Many of the oil fields in Central Sumatra arc associated with paleohighs. drag folds, and post mid- Miocene iiiversion Hydrocarbon generation was initiated during the Miocene and continues currently in some parts of the basin.