Petroleum source rock evaluation and palynofacies analysis of Bongaya formation in Pitas area, Northern Sabah / Nor Aainaa Farhana Md Nor ‘Azam

Nor Aainaa Farhana , Md Nor ‘Azam (2022) Petroleum source rock evaluation and palynofacies analysis of Bongaya formation in Pitas area, Northern Sabah / Nor Aainaa Farhana Md Nor ‘Azam. Masters thesis, Universiti Malaya.

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Abstract

Bongaya Formation is Miocene sediment consisting of mostly sandstone interbedded with shale, coal, and mudstone presence and located on Borneo's northern tip. This study focuses on assessing the organic geochemistry (source rock analyzation, bitumen evaluation, and molecular analysis) of the onshore Bongaya Formation to identify their petroleum hydrocarbon potential. The quantitative pyrolysis technique and petrographic analysis (vitrinite reflectance and maceral counting) are then correlated in the study for better provision where palynology analysis is also conducted to reconstruct the paleoenvironment model of the formation. This work was prompted by the scarcity of geochemical evaluations of the Bongaya Formation in the Pitas area and seismic record suggesting hydrocarbon indicators in the adjacent unexplored offshore basin, which includes the Bongaya Formation (Mazlan et al., 1999). Bulk geochemistry results showed fair to excellent amount of carbon contains, up until 63.1 wt%. The highest TOC value is coals, followed by carbonaceous shales and shale, whereas the lowest (fair) TOC amount is mudstones. The relationship between HI and TOC brings to the identification of kerogen type possessed by Bongaya source rock, as mainly shows Type III kerogen. However, pyrolysis details analysis reveals that there is a possibility of Type II/III kerogen to be present. Bongaya Formation is dominant in generating gas-prone source rock and little oil for some samples, according to intense liptinite occurrence and Py-GC analysis. Petrographic and maceral analysis identified that some of the coal has high resinite constituents, which potentially produce waxy oil. Nevertheless, the variations of Tₘₐₓ data (369.6 –437.3 ˚C) are consistent with huminite reflectance measurements (0.32- 0.43 Rₒ %), indicating that this formation is thermally immature to generate petroleum. The paleoenvironment of organic matter is determined to be colonized by the mangrove area. However, besides mangroves, inland vegetation and back mangrove were also interpreted as a part of the Bongaya Formation depositional environment. The majority of the Bongaya formation was produced from terrestrial organic materials and was primarily maintained in a suboxic environment. There are some indications that some organic materials may be deposited in anoxic conditions, albeit this is not the case in the majority of cases.

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