Source Rock Evaluation and Depositional Environment of Middle Eocene – Early Miocene Sediments in Umuahia and it’s Evirons, Niger Delta Basin, Southeasthern Nigeria.
ABSTRACT
The study area is bounded by latitudes 5027’N and 5034’N, and longitudes 7025’E and 7035’E. It falls within the Northern Niger delta Basin.
The aim of this present study is to evaluate the hydrocarbon potentials of the sediments in the area, determine their age and environment of deposition. To achieve this aim, geochemical analysis (TOC and Rock-Eval) and Palynological studies were carried out on fifteen (15) samples.
Results from the analysis indicates that the total organic carbon (TOC) values of the lignites range from 15.65 – 48.61wt.%, averaging (34.23wt.%), while TOC of shales range from 1.07 – 2.61wt.%, averaging (2.11wt.%).
The genetic potential (GP) of the lignites range from 0.54 to 31.08 mg HC/g rock, averaging (9.13 mg HC/g TOC), and the shales, range from 0.42 to 2.33 mg HC/g TOC, averaging (1.07 mg HC/g TOC).
Hydrogen Index (HI) of the lignites range from 01 to 75 mg HC/g TOC averaging (23.4 mg HC/g TOC), and the shale range from 12 to 85 mg HC/g TOC averaging (42.8 mg HC/g TOC).
The above values indicate that the sediments have moderate to high organic matter concentration with potential to generate gas. Hydrogen Index (HI) versus Oxygen Index (OI) diagram classifies the organic matter in the samples as mainly Type IV with minor Type III kerogen.
HI versus Tmax plot also showed that the shale and lignite fall within the immature and postmature zone. This indicates that the sediments have potential to generate gas at appropriate maturity while the lignites that fall within the postmature level are recycled, and/or contaminated materials.
Tmax and Production Index (PI) of the analysed samples also fall within the thermally immature and post mature organic matter. From Palynofacies studies, the major sporomorphs identified in the samples were pollen grains and spores. These are terrestrial sporomorphs which support type III kerogen.
An age range from middle Eocene – Early Miocene is assigned due to some age diagnostic pollen and spore markers species in the samples such as Pachydermites diederixi, Verrrucatosporites usmensis, Inaperturopollenites hiatus, Psilatriporites rotundus, Magnastriatites howardi in the samples.These species are typical of fresh water swamp forest.
TABLE OF CONTENTS
Title Page I
Certification II
Dedication III
Acknowledgements IV
Abstract V
Table of Contents VI
List of Figures VII
List of Tables VIII
List of Plates IX
CHAPTER ONE: INTRODUCTION 1
1.1 Study area 2
1.2 Previous work 2
1.3 Aim of research 4
1.4 Expected outcomes 4
1.5 Study methodology 7
CHAPTER TWO: GEOLOGIC SETTING 8
2.1 Geology of Niger Delta 8
2.2 Basin Evolution 12
2.3 Stratigraphy 13
CHAPTER THREE: DESCRIPTION OF OUTCROPS 17
3.1 Okahia Uga Outcrop 17
3.2 Kelly Quarry Ohiya 17
3.3 Royal Quarry Ohiya 18
3.4 Umudike Outcrop 18
3.5 Umuariaga Outcrop 21
3.6 Umuokom Amawom 27
3.7 Ebiri Outcrop 27
3.8 Iyi Aga Outcrop 27
3.9 Akpatala Outcrop 28
3.10 Nchara Outcrop 28
3.11 Isieke Outcrop 32
3.12 Ajata road Cut 32
3.13 Ameke Outcrop 32
CHAPTER FOUR: ANALYTICAL METHOD 38
4.0 ANALYTICAL METHOD 38
4.1 Sample preparation 33
4.1.1 Sample for Organic Geochemistry 33
4.1.2 Sample for Palynomorphs Analysis 39
4.1.3 Kerogen Analysis 40
CHAPTER FIVE: RESULTS AND INTERPRETATIONS 41
5.1 Results 41
5.1.1 Total Organic Carbon 41
5.1.2 Rock – Eval Pyrolysis 43
5.1.3 Palynofacies Assemblages 43
5.2 Interpretation 50
5.2.1 Quantity of Organic Matter 50
5.2.2 Types and Quality of Organic Matter 51
5.2.3 Thermal Maturity of Organic Matter 52
5.2.4 Hydrocarbon Source Potential 58
5.2.5 Age Determination and Paleoenvironment of deposition 62
CHAPTER SIX: SUMMARY/CONCLUSION 65
REFERENCE 66
INTRODUCTION
Lignite is one of the four fossil fuel resources found in substantial quantities in southeastern Nigeria. The others are sub-bituminous coal, oil and natural gas. Of the four, lignite was the first to be discovered by the Mineral Survey, (1908) (Orajiaka et al., 1990).
Nigeria has the largest deposits of lignite in Africa. From several recent studies, the reserves is about two (2) billion tonnes, with approximately 650 million tonnes (Mmt) as proven (CIA, OnlineNigeria, 2010).
These lignites are confined to a narrow belt about 16km wide, trending S.W – S.E and extending from the Niger River, in the west, to the Cameroon frontier, east of Calabar, in the east, a distance of about 240km (Fig.1).
Within this belt, lignite seams of variable thickness are exposed sporadically in stream valleys and road cuts. In 1919 lignite was discovered in Umuahia – Okigwe area by Messrs Falk and Hives, Divisional Officers for Owerri and Okigwe respectively (Wilson, 1925).
This lignite belt, of mid-Tertiary age, extends from Orlu in the south-east, through Umuezeala, Umuahia, Nnewi, Oba, in a 20 to 40km – wide belt across the Niger, to Ogwashi, Asaba, Mgbiigliba and Adiase-Uti in Delta State.
The lignites have not yet been fully explored, and recently, the Nigerian government has placed a high priority on utilizing these resources.
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