Discriminating hydrocarbon generation potential of coaly source rocks and their contribution: a case study from the Upper Paleozoic of Bohai Bay Basin, China

Abstract

Although various coaly source rocks widely developed in the Carboniferous–Permian (C–P) of the Bohai Bay Basin, their geochemical characteristics and hydrocarbon generation potential are poorly understood. This study aims to discriminate the contribution of hydrocarbon generation from different C–P coaly source rocks and clarify the differences within generated oils using organic geochemistry, organic petrology, and thermal simulation experiments. The coaly source rocks containt coal clarain and durain, carbonaceous shale, and shale deposited in deltaic and lagoonal environment. The results indicated that clarain, durain, and carbonaceous shale exhibited higher hydrogen index and liquid–gas hydrocarbon yields than lagoonal and deltaic shales, which was mainly associated with the concentrations of sporinite, cutinite, and hydrogen-rich collodetrinite. Aliphatic hydrocarbons originated from coal and carbonaceous shale presented lower Ts/(Ts+Tm), Ga/17α(H)21β(H)-C₃₀ hopane, 18α(H)-oleanane/17α(H)21β(H)-C₃₀ hopane ratios, and higher 17β(H)21α(H)-C₃₀ Morane/17α(H)21β(H)-C₃₀ hopane than deltaic lagoonal shales. Parameters of aromatic hydrocarbons generated from five lithologies of coaly source rocks trended as clear group distribution, e.g., clarain and durain showing lower MNR, DBT/Fluorene (F) ratios and higher DBF/F ratio than coaly shales. The distinct descending trend of hydrocarbon potential is obtained from clarain, durain, carbonaceous shale to lagoonal and deltaic shales, implying dominated the petroleum and natural gas supplement from coal and carbonaceous shale. The difference between aliphatic and aromatic hydrocarbons provides a significant contribution to analyze the generic relationship between coaly source rock and lacustrine shale. Our results illustrate the importance of coaly source rocks for the in-depth oil-gas exploration of the Bohai Bay Basin and understanding hydrocarbon generation potential of source rocks in coal bearing strata.

Graphical abstract

Keywords

thermal simulation / hydrocarbon generation / coaly source rock / Carboniferous–Permian / Bohai Bay Basin

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