Hydrocarbon Generation Potential of Oligocene Oil Shale Deposit at Onshore Penyu Basin, Chenor, Pahang, Malaysia

Abstract

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 % total organic carbon (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. The vitrinite reflectance values are less than 0.5% R o in all of the analyzed samples, indicating low maturity stage. This is corroborated by T max values ranging from 383 to 429 °C. However, based on the kinetic simulation model, the average predicted geological temperature for the onset of hydrocarbon generation is 109 °C, while the peak of hydrocarbon generation is 153 °C. 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 TOC of these oil shales is consistent with that of the Tertiary oil shale deposits in China. The analyzed 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 kerogens’ (mixed oil and gas) generative potential. Similarly, bulk kinetic analysis of the analyzed samples suggests typical petroleum source rock 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 which revealed that the samples are composed mainly of liptinite (sporinite, cutinite, amorphous organic matter, and resinite) and vitrinite, with varied trace amounts of inertinite.

Geochemical Characteristics of Released Organic Matters by Acid Decomposition of Hydrocarbon Source Rocks from Different Sedimentary Basins

“…Meanwhile, the rock-eval pyrolysis technique has been widely applied in evaluating hydrocarbon generation potential [5][6][7], and related index (e.g., HI and OI) can be calculated by pyrolysis parameters to distinguish the types of kerogen. However, some studies indicated that the types of kerogen, which was obtained from HI and OI, may not always accurate [8][9][10]. Therefore, the TOC content, pyrolysis parameters, and other evaluation approaches can be utilized in combination to investigate hydrocarbon generation potential source rocks.…”

Geochemical and organic petrographic characteristics of high bituminous shales from Gurha mine in Rajasthan, NW India

“…Contribution to unconventional oil-shale resources. The properties of the organic-rich shale sediments and their contribution to petroleum-shale resources are generally assessed based on organic type and thermal ripening temperatures 20,21,28,41,44,45 . In this study, the integrated geochemical results and the kerogen microscopic features were discussed to characterize the organic facies and their potential as an oil-shale resource in the bituminous shale-bearing horizons of the Palana Formation in the Bikaner sub-basin of Rajasthan state.…”

Use of Outcrop as Substitute for Subsurface Shale: Current Understanding of Similarities, Discrepancies, and Associated Challenges

“…Broadhead and Rinehart also declared that as the Mancos Shale becomes shallower it becomes thermally immature with very low oil generation potential. Makeen et al also obtained vitrinite reflectance and T max less than 0.5% and 429 °C, respectively, for an immature shale outcrop deposit in Malaysia with a considerably high TOC (>15 wt %).…”

“…Hence, in the absence of subsurface cores, proper outcrop sampling is very important. The candidate samples need to be collected from equivalent outcrops by digging trenches to minimize the potential influence of weathering. ,, Furthermore, as previously discussed, upon dissolution of carbonate and chlorite due to pyrite oxidation, the strength and density of shale formation decline and its porosity increases . Overall, they result in alteration of geomechanical properties of the rock.…”