Organic and inorganic geochemistry of northwestern Niger Delta oils

A detailed geochemical study of oil samples from an onshore field in the Niger Delta was carried out for their characterization and correlation. The samples were analyzed using Gas Chromatographic (GC), Gas Chromatographic-Mass Spectrometric (GC-MS) and Inductively Coupled Plasma-Mass Spectrometric (ICP-MS) analytical techniques. The results showed that CPI, Pr/Ph, Pr/nC17, Ph/nC18 and odd/even ratios ranged from 0.91 to 1.17, 3.07 to 6.04, 0.39 to 0.80, 0.14 to 3.30 and 1.33 to 1.39 respectively. The concentration levels of Co, Cr, Cu, Fe, Ni and V ranged from 0.9 to 32, 6.2 to 24, 3.31 to 19.4, 11.4 to 1241, 26.3 to 144 and 11.0 to 29.7 pbb respectively. The Pr/nC17 vs. Ph/nC18 plot revealed two oil types; non-degraded and minor degraded oils, which were derived from organic matter deposited in transitional environments. This suggests that both oil types have identical source rocks. Also, CPI values of 0.91 to 1.17 indicated that the oils are thermally mature. Biomarker data also discriminated the oils into two groups on the basis of biodegradation and revealed that the oils are mature and generated at almost the same thermal maturity level. The results of Ni vs. V, Co/Ni vs. V/Ni cross plots and cluster analysis similarly revealed identical two oil types. The similarity in the results of both organic and inorganic geochemistry of these oils shows that an integrated organic and inorganic geochemical data provide a reliable tool for the evaluation, characterization and correlation of crude oils.

[1]  D. Karlsen,et al.  Petroleum geochemistry of the Haltenbanken, Norwegian continental shelf , 1995, Geological Society, London, Special Publications.

[2]  S. Larter,et al.  Reservoir geochemistry: methods, applications and opportunities , 1995, Geological Society, London, Special Publications.

[3]  R. Filby,et al.  Neutron activation analysis of Nigerian crude oils , 1993 .

[4]  P. Meyers,et al.  Types and Thermal Maturity of Organic Matter Accumulated During Early Cretaceous Subsidence of the Exmouth Plateau, Northwest Australian Margin: Chapter 8 , 1993 .

[5]  C. Diessel.  Coal Bearing Depositional Systems , 1992 .

[6]  A. Barwise.  Role of nickel and vanadium in petroleum classification , 1990 .

[7]  J. Curiale.  Distribution of Transition Metals in North Alaskan Oils , 1987 .

[8]  J. Nwachukwu,et al.  Organic Matter of Agbada Formation, Niger Delta, Nigeria , 1986 .

[9]  J. Ellrich,et al.  Distribution of trace elements in crude oils from southern Germany , 1985 .

[10]  M. Lewan.  Factors controlling the proportionality of vanadium to nickel in crude oils , 1984 .

[11]  B. Hitchon,et al.  Use of Trace Elements for Classification of Crude Oils into Families--Example from Alberta, Canada , 1984 .

[12]  C. Ndiokwere.  Analysis of nigerian petroleum for trace elements by neutron activation , 1983 .

[13]  M. Lewan,et al.  Factors controlling enrichment of vanadium and nickel in the bitumen of organic sedimentary rocks , 1982 .

[14]  J. Okogun,et al.  Preliminary organic geochemical studies of samples from the Niger delta (Nigeria) I. Analyses of crude oils for triterpanes , 1979 .

[15]  B. D. Evamy,et al.  Hydrocarbon Habitat of Tertiary Niger Delta , 1978 .