Petroleum source rock potential of submarine fan and deltaic cenozoic sequences of Western Sabah and Sarawak, Malaysia / Togunwa Serifat Olayinka

Togunwa Serifat, Olayinka (2015) Petroleum source rock potential of submarine fan and deltaic cenozoic sequences of Western Sabah and Sarawak, Malaysia / Togunwa Serifat Olayinka. Masters thesis, University of Malaya.

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Abstract

The study area is in the northwest Borneo which extends between Sarawak and Sabah, Malaysia. This research present geochemical and petrographical data from outcrop samples distributed in the northern part of Sarawak and western part of Sabah, which are considered amongst areas with many uncertainties in terms of hydrocarbon prospectivity. A total number of sixty samples were analyzed to evaluate the organic matter content, hydrocarbon generating potential, kerogen type, thermal maturity, source input and depositional conditions. The samples were collected from fluvio-deltaic deposits (Meligan, Belait, Miri, Lambir, Tukau formations) and deep water turbidites sediments (West Crocker and Temburong formations) of Eocene to Miocene age. Most of the deltaic sequences samples contain above average levels of organic matter content (TOC >1 wt. %) and possess fair to good hydrocarbon generating potential. The samples from the deepwater turbiditic sequences show poor to fair organic matter content and hydrocarbon generating potential except for few samples from West Crocker formation with significantly higher values of TOC. Based on the dominance of Type III and Type III/IV kerogen within these formations that are supported by low Hydrogen Index (HI) values in the range of 20-150 mg/g HC, as well as low atomic hydrogen to carbon ratios (H/C <1), and pyrolysis-gas chromatography (Py-GC) fingerprints displaying dominance of aromatic compounds over n-alkane/alkene doublets, all of which suggest ability to generate gas rather than oil. However, presence of oil prone Type II/III kerogen is observed in the slump deposits within the West Crocker Formation. The thermal maturity assessment based on pyrolysis Tmax and vitrinite reflectance (VR) indicate an immature to very early mature stage for hydrocarbon generation amongst the Belait, Lambir, Miri and Tukau formations. On the other hand, the West Crocker, Temburong, and Meligan formations are generally mature to late mature corresponding to peak oil and gas generation stages. Distribution of n-alkanes and isoprenoids indicate land derived organic matter source input that were preserved under alternating oxidizing and reducing conditions for all of the studied sequences. This is further supported by palynofacies assemblages (abundance of woody fragments), low total sulphur (TS) content, and based on the source and redox sensitive trace elements such as V, Ni, Cr, Co, Sc concentrations and their ratios.

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