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Mineralogical characterization and preliminary assessment of the hydrocarbon potential of sedimentary rock from the western part of the Central Kongo

Rajae Bouamoud, Adnane El Hamidi, Mohammed Halim, Raphael Mulongo Masamba, Roger Antoine Kobo Nlandu, Said Arsalane


In this work, the mineralogical characteristics and the assessment of the petroleum potential of organic carbon-rich sedimentary rock (CK sample) originating from the western part of the Central Kongo were the subject of a preliminary analysis and the results were compared with those of Moroccan oil shales. The mineralogical characterization was carried out using X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF), Fourier Transform Infra-Red (FTIR) spectroscopy, Thermal Gravimetry/Differential Thermal Analysis (TG/DTA) and Scanning Electronic Microscopy (SEM-EDX). The results show that the examined sedimentary rock contain a significant part of minerals, about 80%, consisting of quartz, clays and pyrite, similar to those frequently found in oil shales. The pyrolysis also indicates the presence of volatile matter between 250 and 580°C, attributed to the Organic Matter (OM) disseminated within the sedimentary rock as was shown in several carbon-rich materials. The detection of pyrite in the CK sample reveals the existence of a reducing environment during the preservation period of OM in the source rock. The assessment of the petroleum potential using the basic Rock-Eval method associated with the elemental analysis and 13C Cross Polarization/Magic Angle Spinning Nuclear Magnetic Resonance (13C CP/MAS NMR) spectroscopy indicated a very good organic richness (TOC=10.77%), very good petroleum potential (S2=80.4 mgHC/g rock) with the sapropelic OM described as type I kerogen (H/C molar ratio of 1.71) characterized by high hydrogen index (HI=746 mgHC/g TOC) and low oxygen index (OI=13 mgCO2/g TOC) values. The Rock-Eval results were confirmed by 13C CP/MAS NMR spectroscopy which shows the exclusive presence of aliphatics. The mineralogical and petroleum characteristics of CK sample show a great resemblance with those of known oil shales such as Moroccan oil shales and its kerogen is probably related to a marine or lacustrine environment which formed in anoxic sedimentary rocks and with a thermal evolution that has just reached the early stage of the oil window.

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