SOURCE ROCK POTENTIAL OF ORGANIC-RICH SHALES IN THE TERTIARY
BHUBAN AND BOKA BIL FORMATIONS,
Md. Farhaduzzaman1*, Wan Hasiah Abdullah1, Md. Aminul Islam2 and M. J. Pearson3
1 Department of Geology, Faculty of Science,
2 Department of Petroleum Geoscience,
Faculty of Science, Universiti
3Department of Geology and Petroleum
Geology,
*Corresponding author, email: farhadgeo@gmail.com
farhad.geo@siswa.um.edu.my
Sandstones in the Miocene Bhuban and Lower Pliocene Boka Bil Formations contain all of the hydrocarbons so far discovered
in the Bengal Basin, Bangladesh. Organic-rich shale intervals in these formations
have source rock potential and are the focus of the present study which is based
on an analysis of 36 core samples from wells in eight gasfields in the eastern
Organic matter is dominated by Type III kerogen with lesser amounts of Type II. TOC is 0.16-0.90 wt % (Bhuban Formation) and 0.15-0.55 wt % (Boka Bil Formation) and extractable organic matter (EOM) is 132-2814 ppm and 235-1458 ppm, respectively. The hydrogen index is 20-181 mg HC/g TOC in the Bhuban shales and 35-282 mg HC/ g TOC in the Boka Bil shales. Vitrinite was the dominant maceral group observed followed by liptinite and inertinite. Gas chromatographic parameters including the C/S ratio, n-alkane CPI, Pr/Ph ratio, hopane Ts/Tm ratio and sterane distribution suggest that the organic matter in both formations is mainly derived from terrestrial sources deposited in conditions which alternated between oxic and sub-oxic. The geochemical and petrographic results suggest that the shales analysed can be ranked as poor to fair gas-prone source rocks. The maturity of the samples varies, and vitrinite reflectance ranges from 0.48 to 0.76 %VRr. Geochemical parameters support a maturity range from just pre- oil window to mid- oil window.
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