Publications

Telisa Formation is a member of the Early Miocene Sihapas Group in Central Sumatra Basin. It was deposited in a marine setting and dominated by shale deposition and fine grain clastic material commonly interpreted to be the top seal of petroleum system in the basin. The Telisa is essential in determining the trap-seal integrity in all oil and gas fields in Rokan Block. It is known that Telisa has four to six thin bedded sand-rich members within it which are proven to be hosts for oil accumulation in five structures including Balam South, Bangko, Petapahan, Kotabatak and Minas Northwest flank. Telisa Formation in the eastern part of Central Sumatra Basin in a strict sense is between sequence boundary 17.5 ma to 13,8 ma. It is an emerging play in Rokan and Central Sumatra Basin. The characteristics of Telisa sand reservoir are thin bedded, fine to very fine sandstone, some exhibit sand shale lamination intercalated by glauconite rich laminae, some also exhibit globigerinids sandstone. Reservoir zone and oil pay definition in the Telisa are not straight forward and each field requires a unique formula or definition according to the local geological characteristics. There are at least two groups of Telisa reservoir characteristics. Reservoir definition in the lower part of Telisa is mimicking the reservoir definition in older formations like Duri and Bekasap, with high shale baseline in GR log around 160-180 API and a reduced total resistivity value compared to Duri dan Bekasap intervals. The upper Telisa interval is characterized by lower GR log shale base line around 100-120 API with low contrast between sand and shale. Core data exhibit stacks of sand shale laminations and correspond to larger drops in total resistivity value. Oil pay definition from log, cutting oil shows and sidewall core samples are challenging and enigmatic due to low contrast and low resistivity pay ranges from 2-6 ohms and inconsistent oil shows, even in the proven perforated productive zone. Further reservoir characterization and oil pay definition in Telisa requires special sets of advance data such as continuous core samples, UV photo, spectral gamma ray, resistivity scanner and other high resolution data acquisition. A new workflow of exploration and formation evaluation is necessary to properly assess and unlock the Telisa formation potential, and it will all begin with a detailed analysis of actual rock in conventional core data.