Sains Malaysiana 44(4)(2015): 571–579

Petroleum Source Rock Properties of the Neogene Bhuban Shales, Bengal Basin, Bangladesh

(Pencirian Punca Batuan Petroleum di Syal Neogene Bhuban, Lembangan Bengal, Bangladesh)

MD. FARHADUZZAMAN¹*, WAN HASIAH ABDULLAH¹ & MD. AMINUL ISLAM²

¹Department of Geology, Faculty of Science, University of Malaya, 50603 Kuala Lumpur

Malaysia

²Department of Petroleum Geoscience, Faculty of Science, Universiti Brunei Darussalam, Gadong BE1410, Brunei Darussalam

Diserahkan: 10 Jun 2013/Diterima: 18 November 2014

ABSTRACT

The present study evaluates the petroleum source rock generation potential of the Neogene Bhuban shales from Bangladesh. Organic geochemical and organic petrological methods were used for analyzing 11 drill core samples from 4 gas fields in the basin. Source rock potential, maceral composition, organic matter abundance, biomarker distribution, thermal maturity, hydrocarbon generation and depositional environment were evaluated. Kerogen in the studied shale samples is classified mainly as Type III with lesser amounts of Type II. Vitrinite is the dominant maceral group observed in the analyzed Bhuban samples followed by liptinite and inertinite. Vitrinite reflectance, Tmax and biomarker parameters indicate the thermal maturity ranges from just pre-oil window to mid-oil window. Based on its total organic carbon (TOC), extractable organic matter (EOM) and hydrogen index (HI), the analyzed Bhuban shales are ranked as mainly poor to fair source rocks but with good gas generation potential. The dominant terrestrial environment prevailed during the deposition of the studied Bhuban shales while the condition was sub-oxic as indicated by cross-plots of pristane versus phytane and sterane versus pristane/phytane ratios.

Keywords: Bengal Basin; Bhuban shale; hopane; hydrocarbon potential; sterane

ABSTRAK

Kajian ini membincangkan penilaian batuan punca bagi petroleum sampel syal Bhuban Neogene dari Bangladesh. Geokimia organik dan petrologi organik telah digunakan untuk menganalisis 11 sampel teras gerudi daripada 4 medan gas di kawasan tersebut. Potensi batuan punca, komposisi maseral, kedapatan bahan organik, taburan petanda biologi, kematangan terma penjanaan hidrokarbon dan persekitaran pengenapan dinilai. Kerogen dalam sampel syal yang dikaji kebanyakannya dikelaskan sebagai Jenis III dengan jumlah Jenis II yang lebih kecil. Vitrinit adalah kumpulan maseral yang dominan dalam sampel Bhuban yang dianalisis diikuti oleh liptinit dan inertinit. Pantulan vitrinit, Tmax dan parameter bio penanda menunjukkan kematangan terma daripada hanya pra-minyak ke tingkap-minyak pertengahan. Berdasarkan data TOC, EOM dan HI, syal Bhuban yang dianalisis kebanyakannya dinilai sebagai miskin ke sederhana sebagai batuan sumber dengan potensi penjanaan gas yang baik. Persekitaran daratan dominan semasa pengenapan syal Bhuban dikaji manakala keadaan pengenapan adalah sub-oksik sebagaimana yang dicadangkan berdasarkan plot pristana melawan fitana dan sterana melawan nisbah pristana/fitana.

Kata kunci: Hopana; lembangan Bengal; potensi hidrokarbon; sterana, syal Bhuban

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*Pengarang untuk surat-menyurat; email: farhad.geo@siswa.um.edu.my