Organic petrology of campano-maastrichtian sediments in the Agbogugu-Leru axis, Anambra Basin, South Eastern Nigeria
Date
2015-02
Authors
Journal Title
Journal ISSN
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Publisher
Federal University of Technology, Owerri
Abstract
Ten rock (n=10) samples were subjected to various geochemical analyses to determine organic petrology and paleoenvironment of early Cretaceous sediments in parts of the southern Anambra Basin. The procedure for the determination of the Total Organic Matter content and Rock Eval pyrolysis were achieved using LECO 600 analyzer with a TOC module. Extractible Organic Matter was determined by the use of Soxhlet Extractor while the biomarker distribution was ascertained with the Gas Chromatography. The results reveal that the Total Organic Content (TOC) of shale samples recovered from the Enugu Shale ranged from 0.72 to 4.94 wt % with an average of 2.64 wt %. Samples recovered from the Mamu Formation have TOC values ranging between 0.76 to 2.11 wt % with an average value of 1.49 wt %. These values essentially exceeded the threshold value of TOC ≥ 0.5 wt % requirements for shale rocks to qualify as petroleum source rocks. The values are therefore, suggestive of good to very good sources rocks. The Hydrogen Index (HI) values of sediments from Enugu Shale ranged between 43 to 547 mgHC/gTOC with an average value of 185.65 mgHC/gTOC, while those recovered from sections of the Mamu Formation have HI value of 27 to 54 mgHC/gTOC with an average value of 39.45 mgHC/gTOC. The corresponding Oxygen Index (OI) values ranging between 15 to 106 mgCO2/gTOC was recorded for Enugu Shale sediments with an average value of 59.2 mgCO2/gTOC. The analyzed sediments of the Mamu Formation on the other hand, revealed values of the range of 26 to 86 mgCO2/gTOC, with average of 49.4 mgCO2/gTOC. These results showed that the Enugu and Mamu Formation sediments are dominated by type III kerogen and mixed type II/III kerogens. The maximum Temperature
(Tmax) ranged from 424 to 4390C with an average of 4320C and 417 to 4410C with an average of 4310C for sediments from the Enugu and Mamu Formations, respectively. These temperature values are indicative of immature to transitionally early mature source rocks. The dominant vitrinite maceral group in the analyzed shale samples ranged between 39 to 59 %; Inertnites, between 11 to 18 % while the liptinites ranged between 9 to 21 %. These bio facies in the shale samples from the Enugu and Mamu Formations were derived from the structural parts of plants that are deficient in hydrogen. The sediments are thus deposited in a suboxic but low PH paleo-depositional environment containing moderately to fairly rich organic matter. This source rock has the potential to generate gas rather than oil given sufficient maturity.
Description
This thesis is for the award of Master of Science (MSc.) in Sedimentary/Petroleum Geology
Keywords
Biofacies, organic, geochemical, source rock, maceral, maturity, Department of Geology
Citation
Obiukwu, E. O. (2015). Organic petrology of campano-maastrichtian sediments in the Agbogugu-Leru axis, Anambra Basin, South Eastern Nigeria (Unpublished Master's Thesis). Federal University of Technology, Owerri, Nigeria