Publications

The Northern Kutai Basin has been considered lacking hydrocarbon prospectivity when it’s compared to the Southern Kutai Basin or the Eastern Kutai Basin where many Neogene reservoir rocks has high hydrocarbons productivity. The Kutai Basin’s sediments are older toward northern and western boundary of the Basin which is the Paleogene sediment was cropping out. In December 1990, LASMO RUNTU Ltd acquired 12,880 km square kilometers of block in the northern part of the Kutai Basin. Hydrocarbon seeps observed from Eocene and Oligocene sections imply active petroleum system within the Eocene of Beriun Formation. Primary target of those exploratory wells was the Middle – Upper Eocene Beriun Formation deltaic sands. In 2009, 19 lines of the new recording 2D seismic survey were shot by Kalimantan Kutai Energy PSC to provide modern data within the West Sangatta Block, Northern Kutai Basin. Those new seismic acquisition surveys hopefully will improve the geological interpretation of all existing data. Incorporation of surface and near surface geological information is obtained from surface geological mapping and shot-holes mudlog (geoseis) survey. This paper tries to re-evaluate the Eocene source rock and hydrocarbon potential from surface rocks (outcrops), near surface (geoseis) and hydrocarbon seepages. The surface Eocene facies in study area were divided into four main units, i.e., Late Eocene Middle Shelf, Late Eocene Coaly Brackish, Late Eocene Brackish, and Late Eocene Fluvial. The analytical methods used in this work are Total Organic Carbon (TOC), pyrolysis Rock Eval, standard gravitational column chromatography for hydrocarbon fractionation, Gas Chromatograph (GC), and Gas Chromatography Mass Spectrometry (GCMS) for gas composition and fingerprint analysis. The second objective is to re-evaluate the Eocene reservoir quality of the rock surface samples, brief provenance analysis of their source sediment, visual porosity and possible depositional environment. The source rocks potential are from Late Eocene Coaly Brackish facies. Mostly samples were dominated by vitrinite maceral, which is formed by fibrous and woody plant fragment and structureless colloids of humic matter. Kerogen type analysis result of organic matter type and thermal maturity indicated mixed Type II and Type III, which are having similarities with subsurface samples at Middle Eocene that performed by previous study of LASMO’s exploration well. Meanwhile, two oil-seepages samples analysis indicated derived from two different type kerogens, containing mix organic matter Type I and terrestrial higher plants of Type II/III. The Late Eocene sandstone reservoirs as far as it has unique characteristics, which has two distinct quality characters, first sandstone characterized by conglomerates facies of alluvial fans which have poor reservoir quality and the second type sandstones characterized by conglomeratic sandstone which are have more clean sandstone that associated with fluvial deltaic sandstone facies that have good porosity.