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Hydrocarbon generative potential of Oligocene oil shale deposit at onshore Penyu Basin, Chenor, Pahang Malaysia


This is the first study that focuses on the evaluation of a newly-discovered oil shale deposit in the eastern Chenor area in the state of Pahang, Malaysia. Previously, this deposit was reported as carbonaceous/coaly mudstone. However, in this study, organic-rich immature carbonaceous mudstone containing above 15 wt % TOC is evaluated as oil shale, and that below 3.5 wt % TOC is termed mudstone. Oil shale and mudstone, which are significant sedimentary facies for oil and gas exploration, were investigated using organic geochemical and petrological methods, as well as Computed Tomography (Micro- CT), pyrolysis and bulk kinetic techniques, to evaluate their hydrocarbon generation potential. corroborated The vitrinite reflectance values are less than 0.5 %Ro in all of the analyzed samples indicating low maturity stage. This is corroborated by Tmax values ranging from 383 to 429 °C. However, based on the kinetic simulation model, the average of predicted geological temperature is 0.62% Ro while the peak of hydrocarbon generation is 1.04% Ro. The extractable organic matter and hydrocarbon contents results show that the oil shale samples possess excellent petroleum potential compared to very good values for the studied mudstone. This is consistent with the plots of TOC content versus extractable organic matter, and hydrocarbon yields versus TOC content, commonly used in estimating the hydrocarbon generative potential of source rocks. The analysed oil shale samples are characterized by a high hydrogen index (HI) of up to 700 mg HC/g TOC (average 517.4 mg HC/g TOC), suggesting oil-prone Type I and Type II kerogens. However, the open pyrolysis-gas chromatography (Py-GC) result of these samples displays a predominance of n-alkene/n-alkane doublets extending to the long range homologous series (C7-C33) with considerably high aromatic compounds, which indicates Type II/III keroges (mixed oil and gas) generative potential. Similarly, bulk kinetic analysis of the analysed samples showing typical petroleum source rocks facies derived from heterogeneous (Type II/III kerogens) organic matter assemblages. Thus, based on the pyrolysis and bulk kinetic result, the studied oil shale can be classified as ‘‘cannel coal’’ derived from terrestrial plants materials. This is supported by organic petrological and Micro-CT studies where the analyzed samples were composed of liptinite (sporinite, cutinite, amorphous organic matter and resinite), with varied trace amounts of vitrinite and inertinite.