Molecular geochemical anatomy of the Paleogene petroleum system in the Dongying Depression, Bohai Bay Basin, NE China and solutions to a range of petroleum geology and earth history problems
Date
2021-06
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Abstract
Geochemical characteristics of petroleum systems are critical for hydrocarbon exploration and production. Multiple source rocks, episodic charges from different source rocks and secondary alteration processes make the petroleum systems complex and difficult to understand in the Dongying Depression, Bohai Bay Basin, NE China. Molecular components of oils and source rock extracts in the Dongying Depression exhibit significant heterogeneity which allows us to decipher the paleo-depositional environments, maturity levels, mixing scenarios and secondary alterations, therefore benefiting further hydrocarbon exploration. This thesis conducted a molecular geochemical anatomy of the Paleogene petroleum system in the Dongying Depression by a series of biomarkers including β-carotane, perylene and alkylbiphenyls. Perylene is widely used as an indicator of highly reducing paleoenvironments. Perylene is however absent or in trace amounts from source rocks of the Es4 Member of the Eocene Shahejie Formation, deposited in saline and reducing conditions, but is present in abnormally high concentrations from source rocks of the Es3 Member with fresh to brackish, less reducing settings. Hence, caution should be taken when perylene is used as an indicator of strongly reducing environments, as perylene may be preserved in oxidizing environments with a possible alternative formation pathway via cyclodehydrogenation of 1,1′-binaphthyl. β-Carotane is widely deposited in saline and reducing lacustrine source rock environments, and has proved to be a valid biomarker in oil-oil and oil-source correlations in the Dongying Depression. Novel parameters derived from β-carotane, including β-carotane/C24 tetracyclic terpane, β-carotane/(C19 + C20) tricyclic terpanes and β-carotane/(18α(H)-22,29,30-trisnorneohopane + 17α(H)-22,29,30-trisnorhopane), were proposed for oil family classification. Additionally, β-carotane is concentrated in the severely biodegraded oils due to biodegradation removing most vulnerable components making β-carotane a stable reference compound to assess the extent of biodegradation. Novel parameters derived from alkylbiphenyls and alkyldiphenylmethanes, consisting of 3-/2-methylbiphenyl (MBP), 4-/2-MBP, 3,4'-/3,3'-DMBP and 3-MBP/3-methyldiphenylmethane (MDPM) are proposed for source rock potential and oil genetic origin assessment. The hydrocarbon exploration potential of the deep Dongying Depression was tentatively investigated using a mixed oil with immature Es4 source and highly mature sources (probably the Mesozoic strata). The highly mature fractions may indicate a new hydrocarbon exploration prospect in the deep Dongying Depression, Bohai Bay Basin.
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Keywords
Organic geochemistry, Petroleum geology, Petroleum system, Thermal maturity, Biodegradation, Biomarkers, β-Carotane, Perylene, Biphenyl
Citation
Wang, Q. (2021). Molecular geochemical anatomy of the Paleogene petroleum system in the Dongying Depression, Bohai Bay Basin, NE China and solutions to a range of petroleum geology and earth history problems (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.