aspects of organic geochemistry of nigerian coal university of ibadan

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ABSTRACT Several studies have suggested that coal can be a potential petroleum source rock in deltaic and other basins of the world. However despite its vast deposits in Nigeria, there is a depth of information on its use as a source-rock of petroleum. This study evaluated the source rock potential of Nigerian coal based on chemical and isotope composition of biomarkers and polycyclic aromatic hydrocarbons in the coals. Twenty-two coal and carbonaceous shale samples were collected from four boreholes in Mamu and Awgu Formations of Lower and Middle Benue Trough, Nigeria. The samples were subjected to Elemental analysis using Carlo Erba 1108 CHNS-O Analyzer. The source rock potential of the samples were determined using Rock-Eval analysis. Biomarkers in the aliphatic and polar fractions and aromatic hydrocarbon distributions in the samples were studied using Gas Chromatography- Mass Spectrometry (GC-MS). The Carbon isotope analysis of individual n- alkanes in the aliphatic fraction was performed using Gas Chromatography-Combustion-Isotope Ratio Mass Spectrometer (GC-IRMS). The vitrinite reflectance measurements of the samples were taken using Zeiss standard universal reflected microscope. All the coals analyzed contained the minimum of 0.5wt.% and 2mg/g of Total Organic Carbon (TOC) and Genetic Potential (GP) respectively of organic matter required to serve as good source rock for oil and gas. Several plots from the elemental and Rock-Eval pyrolysis classified the organic matter in Awgu and Mamu samples as type III and type II/III kerogen respectively. The abundance of hopanes, homohopanes (C31-C35), benzohopanes and C29 steranes and diasteranes in most of the samples indicate terrestrial plant, phytoplankton and cyanobacteria contributions to the organic matter that formed the coal. High (Pr/Ph) ratio (1.73-12.47), distributions of polyaromatic hydrocarbons and isotopic distribution of individual alkanes showed that Awgu samples consisted of mixed terrestrial/marine organic matter deposited under oxic condition in lacustrine- fluvial/deltaic depositional environment. Mamu samples consisted of terrestrial organic matter with marine incursion deposited under oxic/suboxic-oxic in lacustrine-fluvial/deltaic environment. The vitrinite reflectance values (0.48-1.15%Ro) and all the maturity parameters derived from the elemental, Rock-Eval analysis and biomarker distributions showed that Awgu samples are in the late oil window, and Mamu samples have low thermal maturity status. 6
The distribution patterns of C32-C35 benzohopanes in Mamu samples confirmed the redox condition of organic matter deposition within the Formation. The presence of unsaturated oleanenes in Mamu samples further confirmed their thermal immaturity status. The kerogen types of the samples have capacity to generate both oil and gas. Benzohopanes (C32-C35) and three oleanene isomers; olean-12-ene, olean-13 (18)-ene and olean-18-ene were present in samples collected from Mamu Formation. These compounds were detected for the first time in Nigerian coal. Awgu Formation coals might have generated gases into yet-to-be identified reservoir. Coals from Mamu Formation have potential to generate both oil and gas but are presently immature to have formed any significant hydrocarbons. Keywords: Biomarkers, Carbonaceous shale, Benue-Trough, Carbon Isotopes, Hydrocarbon potential. Word count: 460. 7
Page 1 and 2: ASPECTS OF ORGANIC GEOCHEMISTRY OF
Page 3 and 4: ACKNOWLEDGEMENTS All praises are du
Page 5: CERTIFICATION This is to certify th
Page 9 and 10: 1.6.3.2 Biomarker Analysis………
Page 11 and 12: 4.1.1.2 Mamu Formation…………
Page 13 and 14: Fig.4.3: Plots of S2 vs. TOC of Coa
Page 15 and 16: Fig.4.36: m/z 156, 170 Mass chromat
Page 17 and 18: 1.1 Introduction CHAPTER ONE INTROD
Page 19 and 20: 1.2.2 Coalification This is the pro
Page 21 and 22: The longer the aliphatic chains the
Page 23 and 24: Fig. 1.1 : Location of Anambra Basi
Page 25 and 26: 1.6 Petroleum Source Rock Evaluatio
Page 27 and 28: The type II kerogen has relatively
Page 29 and 30: Organic petrographers also develope
Page 31 and 32: 2.1 Biomarker Geochemistry CHAPTER
Page 33 and 34: However, the ratio is known to be a
Page 35 and 36: Generally, short chain n-fatty acid
Page 37 and 38: Their derivatives were reported onl
Page 39 and 40: Fig. 2.1 (contd.): Chemical structu
Page 41 and 42: Sponges are the only marine organis
Page 43 and 44: The use of α-and β- amyrins as te
Page 45 and 46: High abundance of C35 hopane usuall
Page 47 and 48: Fig. 2.2: Transformation of sterane
Page 49 and 50: A variety of aromatic maturity para
Page 51 and 52: more stable β-substituted isomer (
Page 53 and 54: Also, it has been shown that n-alka
Page 55 and 56: The distribution pattern of individ
Page 57 and 58:
2.3.3 Sulphur Isotopes Sulphur isot
Page 59 and 60:
2.4.1.1 Flash or Rapid temperature-
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S2 S1 Free hydrocarbon, FID Hydroca
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2.4.2 Gas chromatography/Mass spect
Page 65 and 66:
Based on the comparison of δD valu
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Fig. 2.4 :Geological map of Benue T
Page 69 and 70:
The shale limestone sequence formed
Page 71 and 72:
CHAPTER THREE EXPERIMENTAL 3.1 SAMP
Page 73 and 74:
Fig. 3.2: Lithographic section of O
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3.1.5 Derivatisation of Polar fract
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3.2.5. Gas chromatography-isotope r
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4.1.1.2 Mamu Formation The C conten
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Fig. 4.1: Plot of Atomic H/C agains
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Samples Awgu Formation LB387 Lithol
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Fig. 4.2 : Plots of HI vs OI of Coa
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Fig. 4.3 : Plots of S2 vs TOC of Co
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Vitrinite reflectance values were e
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Fig. 4.6 : Plots of HI vs Tmax of C
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4.3 Biomarker Geochemistry of the N
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Fig. 4.8 (contd.): m/z 85 Mass chro
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Fig. 4.9 (contd.): m/z 85 Mass chro
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Fig. 4.10 (contd.): m/z 85 Mass chr
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Fig. 4.11: Plots of Pr/nC17 against
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4.3.1.2 Mamu Formation The n-alkane
Page 105 and 106:
Fig. 4.13: m/z 74 mass chromatogram
Page 107 and 108:
Page 109 and 110:
Fig. 4.15 (contd.): m/z 74 mass chr
Page 111 and 112:
Page 113 and 114:
Table 4.4: Parameters calculated fr
Page 115 and 116:
Various ratios of tricyclic terpane
Page 117 and 118:
Fig. 4.20: m/z 191 showing the dist
Page 119 and 120:
Sample Table 4.5 : Tri- and tetracy
Page 121 and 122:
The ratio values (
Page 123 and 124:
Fig. 4.23 : m/z 191 Mass chromatogr
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Table 4.6 : Peak identities on m/z
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Samples Awgu Formation Depth (m) Ta
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4.3.4.2 Mamu Formation The C27 to C
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Fig. 4.26: Mass frangmentogram and
Page 133 and 134:
Three isomers of oleanenes; olean-1
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Fig. 4.28 : m/z 217 mass chromatogr
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Page 139 and 140:
Fig. 4.31 : Ternary plots of C27, C
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Fig. 4.33 : Plots of 22S/22S+22R C3
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The 20S/20S+20R and αββ/αββ+
Page 145 and 146:
Fig. 4.34 : m/z 156, 170 mass chrom
Page 147 and 148:
Page 149 and 150:
Page 151 and 152:
Various maturity parameters calcula
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Fig. 4.38 : m/z 178, 192, 206 mass
Page 155 and 156:
Page 157 and 158:
Fig. 4.40 :Organic matter source di
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4.4.3.1 Awgu Formation Dibenzothiop
Page 161 and 162:
Fig. 4.41 (contd.): m/z 184,198,212
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Fig. 4.42 : Cross plot of total Sul
Page 165 and 166:
Fig. 4.44 : Cross plot of dibenzoth
Page 167 and 168:
4.4.3.2 Mamu Formation The dibenzot
Page 169 and 170:
Table 4.14: Carbon Isotopic Composi
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4.5.1.2 Mamu Formation The δ 13 C
Page 173 and 174:
Fig. 4.47: Carbon isotopic distribu
Page 175 and 176:
CHAPTER FIVE SUMMARY AND CONCLUSION
Page 177 and 178:
REFERENCES Abubakar, M.B., Obaje, N
Page 179 and 180:
Barthlot, W., Neinhuis, C., Cutler,
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oil and gas, a case study from the
Page 183 and 184:
Chemical Geology 20:205-221. Cranwe
Page 185 and 186:
Ellis, V.O., De Baroos, A.M.A., De
Page 187 and 188:
Geochimica et Cosmochimica 43:739-7
Page 189 and 190:
Kleemann, G., Poralla, K., Englert,
Page 191 and 192:
Mackenzie, A.S. 1984. Application o
Page 193 and 194:
Norgate, C. M., Boreham, C. J. and
Page 195 and 196:
Peters, S.W. 1982.Central West Afri
Page 197 and 198:
Revill, A.T., Volkman, J.K., O’Le
Page 199 and 200:
Schwark, L. Vliex, M. and Schaeffer
Page 201 and 202:
Stefanova, M., Markova, K., Marinov
Page 203 and 204:
Cosmochimica Acta 56: 1231-1246. Va
Page 205 and 206:
Wen, Z., Ruiyog, W., Radke, M., Qin
Page 207 and 208:
Fig. 4.8 : m/z 85 Mass chromatogram
Page 209 and 210:
Fig. 4.9 : m/z 85 Mass chromatogram
Page 211 and 212:
Fig. 4.10 : m/z 85 Mass chromatogra
Page 213 and 214:
Page 215 and 216:
Page 217 and 218:
Fig. 4.15 (contd.): m/z 74 mass chr
Page 219 and 220:
Page 221 and 222:
Fig. 4.19 :m/z 191 showing the dist
Page 223 and 224:
Fig. 4.21 : m/z 191 showing the dis
Page 225 and 226:
Fig. 4.23 : m/z 191 Mass chromatogr
Page 227 and 228:
Page 229 and 230:
Page 231 and 232:
Fig. 4.34 (contd.): m/z 156, 170 ma
Page 233 and 234:
Page 235 and 236:
Fig. 4.38 : m/z 178, 192, 206 mass
Page 237 and 238:
Fig. 4.41: m/z 184,198,212,226 mass
Page 239:
239
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