Organic matter characteristics and hydrocarbon generating potential of the Miocene Belait Formation, Brunei-Muara district, Brunei Darussalam

Xihu Sag is the largest petroliferous sag in China offshore area, which is also the main oil and gas exploration battlefield in the East China Sea shelf basin. Source rock is the main material basis for oil and gas generation, its study has important significance on oil and gas exploration in Xihu Sag. By taking source rock of the Eocene Pinghu Formation and Oligocene Huagang Formation of Pingbei area in Xihu Sag as the research object, static characteristics of source rock in Pingbei Area are evaluated and analyzed in the following three aspects: organic matter abundance, types and maturity. The results show that, based on the organic matter abundance, lower member of Pinghu Formation has a high organic matter abundance, mainly gas, while lower member of Huagang Formation is mainly medium-better source rock, with a common hydrocarbon generating potential. Based on the organic matter types, Huagang Formation and Pinghu Formation are mainly type II and type III kerogen, having a certain hydrocarbon generating potential. While, from the point of view of maturity, lower member of Pinghu Formation is under low mature - mature stage, and the lower part of Huagang Formation mainly under mature to high mature stage. Its hydrocarbon generation peak is basically at present.

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Source rock characteristics and hydrocarbon generation potential in Brunei-Muara district, Brunei Darussalam: a comparative case study from selected Miocene-Quaternary formations

Journal of Petroleum Exploration and Production Technology ◽

10.1007/s13202-021-01142-0 ◽

2021 ◽

Vol 11 (4) ◽

pp. 1679-1703

Author(s):

Liyana Nadiah Osli ◽

Mohamed Ragab Shalaby ◽

Md. Aminul Islam

Keyword(s):

Organic Matter ◽

Source Rock ◽

Vegetation Index ◽

Oil And Gas ◽

Vitrinite Reflectance ◽

Rock Properties ◽

Comparative Case Study ◽

Hydrocarbon Generation ◽

Brunei Darussalam ◽

Potential Source Rock

AbstractA comparative analysis on source rock properties has been carried out on the Miocene-Pliocene formations as well as the Quaternary terrace deposits using Rock–Eval pyrolysis results and organic petrography as well as some biomarkers results. Samples were obtained from outcrops of the Quaternary terrace deposits, Pliocene-aged Liang Formation together with the Miocene Miri and Setap Shale formations in Brunei-Muara district, with sample lithologies ranging from coal, coaly shale, shale and lignitic sand. High total organic carbon (TOC) and S2 values ranging from 41.8 to 62.4% and 7.40 mg HC/g rock to 122 mg HC/g rock, respectively, are identified in coals of the terrace deposit, Liang and Miri formations, making these as the best potential source rock due to the “good to excellent” generating potential. Meanwhile, a “fair to poor” potential is exhibited for the coaly shale, shale and lignitic sand samples as a result of their low TOC, HI and S2 values. The organic matter is composed of kerogen type III (gas prone) and type II-III (mixed oil and gas prone). Organic matter in all studied formations originate from a terrestrial-source, as proven by the abundance of huminite. Organic petrographical and biomarkers studies suggest that the coals and lignitic sand samples were deposited in a mangrove-type mire in a lower delta setting, under oxic and limnic to limnotelmatic conditions, except sample DD2-1, which is deposited in a less water-saturated environment. The samples display the presence of bi-modal and normal distribution of n-alkanes. For all of the samples, the dominating plant types in the palaeomire are of soft, herbaceous plants and this is supported by the low vegetation index and moderate Paq values. All the studied samples are thermally immature to early mature, as exhibited by the Tmax values that range from 300 to 437 °C and vitrinite reflectance readings of 0.22% to 0.46%.

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