Based on field work supported by laboratory analyses of samples from Upper Kutai Sub-basin has resulted sedimentation succession initially in Early Cretaceous-Early Eocene that produced sediments dominated by fluvial deposits (Kiham Haloq Formation). Up-wards, the sediments were continued as fluvial-deltaic deposits system of Batu Kelau Formation deposited in Middle Eocene, fluvial-deltaic to shallow marine system of Batu Ayau Formation deposited in Middle to Late Eocene, and shallow marine deposits that consist of sandstone, marine massive shale, and limestone in Early to late Oligocene (Ujoh Bilang Formation). Several potential reservoir rocks indentified in Upper Kutai Sub-Basin include sandstones facies of Kiham Haloq Formation (fluviatile), deposited in Paleocene (porosity 5 – 8%), fluvial – deltaic sandstone facies of Batu Ayau Formation in Middle – Late Eocene (porosity 13 – 29%, permeability 1.2 – 268 mD), Limestone facies of Batu Ayau Formation in Late Eocene (porosity 4 – 8%), lanmering shallow marine sandstone facies of Ujoh Bilang Formation in Oligocene (porosity 14.1%, permeability 0.58 mD). Porosity types that developed within sandstone reservoirs are primary interparticle, secondary dissolution and micro-pores that produced from decaying of unstable grains due to alteration soon after depositional process. Whereas in limestone reservoir porosity that is developed include dissolution such as pint point, mouldic and vugular pore types. Key
Key words : Upper Kutei Sub-Basin, Formation, potential reservoir rocks, sandstone, limestone, porosity.
Author : Agus Priyantoro, Engkus Kusmana, Andi Ruswandi