SURFACE DATA RE-EVALUATION, EOCENE SOURCE ROCK POTENTIAL AND HYDROCARBON SEEPAGE, AND EOCENE SAND RESERVOIR PROSPECTIVITY IN WEST SANGATTA, NORTHERN KUTAI BASIN

摘要

The Northern Kutai Basin has been considered lacking hydrocarbon prospectivity when it’s compared to the Southern Kutai Ba sin or the Eastern Kutai Basin where many Neogene reservoir rocks has high h ydrocarbons 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 b lock 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 th e 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 s urface and near surface geological information is obtained from surface geological mapping and shot-holes mudlog (geoseis) survey. This paper tries to re-ev aluate the Eocene sourc e rock and hy drocarbon potential from surface rock s (outcrops), near surface (geoseis) and hydrocarbon seepages. The surfa ce 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 L ate 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 co mposition 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 r ocks potential are fro m 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 hum ic matter. Kerogen type analy sis 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 w ell. Meanwhile, two oil- seepages samples analysis indicated derived from two different type kerogens, containing mix organic matter Type I and terrestrial higher pla nts of Type II/III. The Late Eocene sandstone reservoirs as far as it has unique charact eristics, 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 associ ated with fluvial deltaic sandstone facies that have good porosity.