i SEISMIC STUDY OF THE ORANGE BASIN, OFFSHORE NAMIBIA AND ITS RELEVANCE FOR HYDROCARBON SYSTEM ANALYSIS A THESIS SUBMITTED IN FULFILLMENT OF THE REQUIREMENT FOR THE DEGREE OF MASTER OF SCIENCE IN GEOLOGY OF THE UNIVERSITY OF NAMIBIA By Victoria Sibeya Student Number: 9819509 November 2014 Main Supervisor: Dr. Ansgar Wanke ii ABSTRACT The Orange Basin is located on the South-west African continental margin adjacent to the boundary between South Africa and Namibia. The interpretation of the existing 2D seismic and well data using Petrel software provided a structural and stratigraphic analysis of the Orange Basin. The objective of the study is to identify and characterize the regional petroleum systems and reveal the sequence of depositional events and structural developments which occurred in the Basin. Four major tectonostratigraphic units separated by three major unconformities were identified as Pre-rift (Carboniferous to early Permian), Syn-rift (late Jurassic to Hauveterivian), Early drift (Barremian to Cenomanian) and Late Cretaceous (Turonian to recent). The stratigraphic analysis of seismic data revealed a number of depositional features such as clinoforms, channels and palaeo highs which were used to depict different depositional environments in the Basin. Onshore analogues such as the aeolian/lava deposits of the Huab Basin, Kalkrand Formation, Ganigobis Shale Member, Whitehill Formation and Orange River Mouth deposits provides an insight into the depositional history of the Orange Basin. There is a complete petroleum system in Orange Basin which consists of a lacustrine Synrift section, succeeded by Barremian to early Aptian and Cenomanian-Turonian source rocks. Three potential reservoir intervals have been identified, one in the lacustrine Synrift section, the second in aeolian/lava deposits of the Barremian section and the youngest one in Tertiary sandstones. The Orange Basin exhibits both, stratigraphic and structural traps. Deep marine Cretaceous to Tertiary shales are iii predicted to act as seals in the Pre-rift, Syn-rift and Drift sequences. Less faulted Cretaceous and Tertiary shales reveal a good quality seal. Faulting augments the migration pathway of hydrocarbons in the Basin. The southern part of the Basin is considered to be more prospective because it attains thick sediment accumulations which augment source rock maturity and contains most of the stratigraphic and structural closures in the Basin. iv ACKNOWLEDGEMENT I would first like to express my most sincere gratitude to my supervisor Dr. Ansgar Wanke, for his support and supervision offered in every aspect of my studies towards this Thesis. The encouragements and assistance rendered with many constructive discussions contributed greatly to the success of this study. A special thank you goes to the National Petroleum Corporation of Namibia (NAMCOR) Ltd, for supplying data used in this study and also partially funding the Orange River field-trip. Finally, I would like to thank Schlumberger for donating Petrel software to the University of Namibia which was used for this study. v DECLARATION I, Victoria Sibeya, declare hereby that this study is a true reflection of my own research, and that this work, or part thereof has not been submitted for a degree in any other institution of higher education. No part of this thesis may be reproduced, stored in any retrieval system, or transmitted in any form, or by means (e.g. electronic, mechanical, photocopying, recording or otherwise) without the prior permission of the author, or The University of Namibia in that behalf. I, Victoria Sibeya, grant the University of Namibia the right to reproduce this thesis in whole or in part, in any manner or format, which the University of Namibia may deem fit, for any person or institution requiring it for study and research; providing that The University of Namibia shall waive this right if the whole thesis has been or is being published in a manner satisfactory to the University. …………………………… …………………….. Victoria Sibeya Date vi TABLE OF CONTENTS ABSTRACT ................................................................................................................ ii ACKNOWLEDGEMENT ........................................................................................ iv DECLARATION ........................................................................................................ v LIST OF FIGURES ................................................................................................... x LIST OF TABLES ................................................................................................... xx CHAPTER 1: INTRODUCTION ............................................................................. 1 1.1 BACKGROUND TO THE RESEARCH ....................................................................... 1 1.2 EXPLORATION HISTORY ...................................................................................... 3 1.3 STATEMENT OF THE PROBLEM ............................................................................. 8 1.4 OBJECTIVES OF THE STUDY ................................................................................. 8 CHAPTER 2: LITERATURE REVIEW ............................................................... 10 CHAPTER 3: MATERIAL AND METHODOLOGY ......................................... 22 3.1 AVAILABLE DATA .............................................................................................. 22 3.2 INTERPRETATION APPROACH ............................................................................ 25 3.2.1 Data analysis ............................................................................................. 25 3.2.2 Seismic to well tie ...................................................................................... 28 3.2.3 Stratigraphic analysis ............................................................................... 32 i.Seismic Facies Analysis ............................................................................... 36 ii. Identification of System Tracts .................................................................. 41 3.2.4 Structural Analysis .................................................................................... 44 vii 3.2.5 Petroleum System ...................................................................................... 45 3.2.6 Onshore Analogues ................................................................................... 45 CHAPTER 4: RESULTS AND ANALYSIS .......................................................... 47 4.1 STRATIGRAPHIC ANALYSIS ............................................................................... 47 4.1.1 Well Correlation ....................................................................................... 47 4.1.2 Overview of the Orange Basin .................................................................. 53 4.1.3 Stratigraphic Framework .......................................................................... 57 4.1.3.1 Pre-Rift (Carboniferous to Mid Jurassic) ........................................... 57 i. Structural History Review ....................................................................... 57 ii. Depositional Review .............................................................................. 59 iii. Seismic Interpretation (own observations) ........................................... 60 4.1.3.2 Syn-Rift ............................................................................................ 62 i. Structural History Review ....................................................................... 62 ii. Depositional Review .............................................................................. 63 iii. Seismic Interpretation (own observations) ........................................... 63 4.1.3.3 Early Drift ......................................................................................... 65 i. Structural History Review ....................................................................... 65 ii. Depositional Review .............................................................................. 65 iii. Seismic Interpretation (own observations) ........................................... 66 iv. Seismic facies (own observation) ......................................................... 66 4.1.3.4 Late Drift........................................................................................... 69 i. Structural History Review ....................................................................... 69 ii. Depositional Review .............................................................................. 69 iii. Interpretation (own observations) ......................................................... 70 viii iv. Seismic Facies (own observations) ....................................................... 71 4.2. Summary ...................................................................................................... 80 4.3 STRUCTURAL MAPPING ............................................................................. 85 4.3.1 Base Barremian ......................................................................................... 85 4.3.2 Mid-Aptian ................................................................................................ 88 4.3.3 Turonian Unconformity ............................................................................. 92 4.3.4 Top Santonian Unconformity .................................................................... 95 4.3.5 Base Tertiary Unconformity .....................................................................