The petroleum geochemistry of the Termit Basin,Eastern Niger |
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| Institution: | 1. Research Institute of Petroleum Exploration and Development, PetroChina, 100083 Beijing, China;2. Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, 510640 Guangzhou, China;1. Department of Geology, University of Malaya, 50603 Kuala Lumpur, Malaysia;2. National Centre for Petroleum Research and Development, A.T.B.U, Bauchi State, Nigeria;3. Geology Department, Faculty of Applied Science, Taiz University, 6803, Taiz Yemen;4. Department of Geology, Ekiti State University, P.M.B. 5363, Ado-Ekiti, Nigeria;1. Department of Applied Geology, The Federal University of Technology, P.M.B. 704 Akure, Nigeria;2. Department of Geological Sciences, Osun State University, P.M.B. 4494, Osogbo, Nigeria |
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| Abstract: | Sixty crude oils from the Termit Basin (Eastern Niger) were analysed using biomarker distributions and bulk stable carbon isotopic compositions. Comprehensive oil-to-oil correlation indicates that there are two distinct families in the Termit Basin. The majority of the oils are geochemically similar and characterized by low Pr/Ph (pristane to phytane ratios) and high gammacerane/C30 hopane ratios, small amounts of C24 tetracyclic terpanes but abundant C23 tricyclic terpane, and lower δ13C values for saturated and aromatic hydrocarbon fractions. All of these geochemical characteristics indicate possible marine sources with saline and reducing depositional environments. In contrast, oils from well DD-1 have different geochemical features. They are characterized by relatively higher Pr/Ph and lower gammacerane/C30 hopane ratios, higher amounts of C24 tetracyclic terpane but a low content of C23 tricyclic terpane, and relatively higher δ13C values for saturated and aromatic hydrocarbon fractions. These geochemical signatures indicate possible lacustrine sources deposited under freshwater, suboxic-oxic conditions. This oil family also has a unique biomarker signature in that there are large amounts of C30 4α-methylsteranes indicating a freshwater lacustrine depositional environment.The maturity of the Termit oils is assessed using a number of maturity indicators based on biomarkers, alkyl naphthalenes, alkyl phenanthrenes and alkyl dibenzothiophenes. All parameters indicate that all of the oils are generated by source rocks within the main phase of the oil generation stage with equivalent vitrinite reflectance of 0.58%–0.87%. |
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| Keywords: | West African Termit Basin Oil family Biomarkers GC–MS analysis |
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