ABSTRACT
Reservoir quality assessment and characterization of sandstone units was carried out across the Afikpo area of the Southern Benue Trough. The study involved field investigations and laboratory studies/analyses. Field samples were subjected to Grain Size Analysis (GSA), Sand Equivalent test and Methylene Blue test. Studies revealed that the sandstones are friable, cross-bedded and show coarsening upward motif. Results from lithofacies analysis indicate seven (7) lithofacies deposited in a low to high energy environment. They are (1) Dark Gray Shale facies (Micaceous Dark Gray Shale Facies and Fossiliferous Dark Gray Shale Facies), (2) Bioturbated Sandstone Facies, (3) Wave Rippled Sandstone Facies, (4) Cross Stratified Sandstone Facies, (5) Horizontal/Laminated Sandstone Facies (6) Heterolithic Sandstone Facies, and (7) Pebbly/Conglomeritic Sandstone Facies. The Micaceous Dark Gray Shale Facies belongs to the Eze-Aku Group while other liithofacies are of the Nkporo Group. Granulometric analysis of sand samples indicates sediments that are poorly to well sorted, generally positively to very positively skewed and mesokurtic to leptokurtic. Results from bivariate plots indicates river sand deposition while multivariate plots indicate the sediments are fluvial and deposited in a shallow marine environment. Out of 18 locations sampled, 13 locations had Sand Equivalent values ranging between 90% – 99%, 4 locations had values between 80% – 89% and one location had 77%. These results indicate that a high number of the samples contained little clay because the higher the Sand Equivalent values, the cleaner the sands. The Methylene BlueF test revealed that the clays contained in the samples are not susceptible to moisture (do not swell) as they had Methylene BlueF values ranges of 1.7g/kg and 3.3g/kg. These values do not exceed the Methylene BlueF limit which is 10g/kg. Permeability results range from 35.07mD to 4112.56mD indicating moderate to excellent reservoir while porosity values indicate poor to good with value range of 7.0 – 15.7%. Regression analyses showed a good correlation between porosity and permeability with R2 (coefficient of correlation) being 74.6%. There was a weak correlation between Sand Equivalent and Methylene BlueF Tests with R2 being 39.5%. Thus, combining results derived from the various analyses, sandstones within the study area possess good reservoir qualities especially to house gas hydrocarbon.
TABLE OF CONTENTS
Title Page I
Approval Page II
Dedication III
Acknowledgement IV
Abstract V
Table of Contents VI
List of Figures X
List of Tables XIII
CHAPTER ONE: INTRODUCTION 1
1.1 Background Information 1
1.2 Location and Accessibility of the Study Area 3
1.3 Study Objectives 3
1.4 Scope and Methodology 5
1.4.1 Preliminary Study 5
1.4.2 Detailed Mapping 6
1.4.3 Laboratory Analyses 6
1.5 Literature Review 7
CHAPTER TWO: GEOLOGICAL SETTING 9
2.1 Regional Geographic Setting 9
2.1.1 Topography 9
2.1.2 Drainage 9
2.1.3 Climate 13
2.1.4 Vegetation 18
2.2 Regional Stratigraphic Setting 21
2.2.1 Tectonic Setting 21
2.2.2 Stratigraphic Setting 24
CHAPTER THREE: FACIES DESCRIPTION 29
3.1 Rock Facies 29
3.2 Dark Gray Shale Facies 33
3.2.1 Micaceous Dark Gray Shale Facies 33
3.2.1.1 Interpretation 35
3.2.2 Fossiliferous Dark Gray Shale Facies 35
3.2.2.1 Interpretation 35
3.3 Bioturbated Sandstone Facies 36
3.3.1 Interpretation 36
3.4 Wave Rippled Sandstone Facies 36
3.4.1 Interpretation 39
3.5 Trough Cross Stratified Sandstone Facies 39
3.5.1 Interpretation 39
3.6 Herring-bone Cross Stratified Sandstone Facies 39
3.6.1 Interpretation 41
3.7 Tabular Cross Stratified Sandstone Facies 41
3.7.1 Interpretation 41
3.8 Horizontal/Laminated Sandstone Facies 41
3.8.1 Interpretation 41
3.9 Heterolithic Facies 41
3.9.1 Interpretation 45
3.10 Pebbly/Conglomeritic Sandstone Facies 45
3.10.1 Interpretation 45
3.11 Lithofacies Correlation 64
3.12 Lithofacies Association 66
3.13 Depositional Model 68
CHAPTER FOUR: SEDIMENTOLOGICAL ANALYSIS 69
4.1 Introduction 69
4.2 To prepare Methylene Blue 70
4.3 Laboratory Tests 70
4.3.1 Samples Tested 70
4.3.2 Sand Equivalent Test 70
4.3.2.1 Sand Equivalent Test Apparatus 70
4.3.2.2 Procedure 72
4.3.2.3 Calculations 74
4.3.2.4 Precautions &n
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