| Summary: | Central Sumatra Basin is an oil reserve basin which is currently exploited by PT. Chevron Pacific Indonesia (CPI). Exploration is still ongoing in Lower Red Bed Formation of Pematang Group, North Aman Trough, Central Sumatra Basin, conducted. Formation evaluation is applied to Badut-1 well of Badut Field and Arwana-1 well in Arwana Field to determine hydrocarbon potential of Lower Red Bed Formation. The outcomes of formation evaluation, including shale volume, porosity, and water saturation, are used to observe porosity and water saturation distribution in the formation, to determine hydrocarbon reservoir zones, and to lithocorrelate both wells thus the continuity can be observed. Porosity is calculated from porosity sonic and porosity density for Badut-1 well, and porosity sonic only for Arwana-1 well. Water saturation is calculated by Modified Simandoux equation. In order to simplify the reservoir analysis, Lower Red Bed Formation of Badut-1 well is divided into zone A, B, and C, and Arwana-1 well is divided into zone I, II, III, and IV. Observation results indicate hydrocarbon potential scattered in Lower Red Bed Formation of Badut-1 well and Arwana-1 well, especially in zone A and zone II. Zone A consists of clean sands with low water saturation. Zone II consists of shaly-sand reservoars with various thickness and water saturation value. Net pay to gross ratio for Badut-1 well is 0.268 and for Arwana-1 well is 0.094. Lithocorrelation also indicates the continuity between two wells.
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