Investigation on the use of diamondoids to determine the origin, type, depositional environment and extent of thermal maturity of source rocks from different oil wells in the Niger Delta was carried out. These were done to evaluate the significant of diamondoids in petroleum exploration in the basin.Samples were obtained from four oil wells (Wells AW, OP, GB and OT) in the Niger Delta. Shale samples were selected using a combination of geophysical well log and visual examination. Pulverized samples were extracted with Soxhlet extraction method and the saturated hydrocarbon fraction was analysed for biomarkers using gas chromatography-mass spectrometry (GC-MS) while the diamondoids content was analyzed using GC-MS-MS. The distribution of tricyclic terpanes, hopanes, regular C27-C29 steranes, n-alkanes and acyclic isoprenoid hydrocarbons showed that samples from well AW were sourced from mixed marine/terrestrial organic matter while those from wells OP, GB and OT consist of organic matter largely from terrestrial origin. The values of Pr/Ph ratio for source rock samples from wells AW and OP indicate deposition of the organic matter under suboxic conditions while those of wells GB and OT were deposited under anoxic conditions. Sterane and hopane biomarker maturity geochemical parameters indicated that the source rock samples from the four wells are thermally mature with maturity level ranging from early to main oil window. Investigation of the origin using diamondoids; ethyl adamantane index (EAI) and dimethyl diamantane index (DMDI) indicated that organic matter of source rock samples from well AW were sourced from mixed marine/terrestrial organic matter, while samples from wells OP, GB, OT sourced from terrestrial organic matter, which is perfect agreement with the results other source geochemical parameters. Assessment of the thermal maturity of the samples using diamondoid maturity parameters; methyl adamantane index (MAI), dimethyl adamantane index (DMAI) and trimethyl adamantane index (TMAI) showed that all the samples from the four wells are thermally mature with maturity level ranging from early to main oil window.

Diamondoid geochemistry of Niger Delta petroleum source rocks

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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