Browsing by Author "Wang, Qianru"

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    Correlation of Maturity Parameters Derived from Methylphenanthrenes and Methyldibenzothiophenes in the Carboniferous Source Rocks from Qaidam Basin, NW China
    (2019-12-21) He, Chuan; Huang, Haiping; Wang, Qianru; Li, Zongxing
    Twenty-one core samples from the Carboniferous Keluke Formation in the Qaidam basin, NW China, have been geochemically characterized to investigate thermal maturation influence on the evolution behaviors of aromatic hydrocarbons and the validity of commonly used maturity parameters. The Keluke Formation was deposited in marine to continental transitional facies and dominated by type III kerogen. Rock-Eval and vitrinite reflectance () measurement suggested that the studied samples are highly matured at peak oil to gas condensate generation stages. Most biomarkers lost their sensitivity to indicate maturity level due to either approaching the equilibrium point or too low concentrations, while isomer distributions in alkylnaphthalenes, alkylphenanthrenes, and alkyldibenzothiophenes still show systematic variations with increasing maturity. The present study focused on the maturity parameters derived from methylphenanthrenes (MP) and methyldibenzothiophenes (MDBT). The most widely used methylphenanthrene index 1 () shows no correlation with known maturity indicators, but the methylphenanthrene ratio () and methyldibenzothiophenes ratio () increase steadily with increasing maturity levels and are proved to be valid maturity parameters. However, empirical vitrinite reflectance estimations derived from MPR and MDR have dramatically overestimated the maturity levels. Our quantitative data illustrated that concentrations of thermally stable isomers (3-MP, 2-MP, and 4-MDBT) increase continuously with increasing maturity while thermally unstable isomers (9-MP, 1-MP, and 1-MDBT) are almost invariable in the studied maturity range. The invalidity of MPI-1 is caused by the involvement of phenanthrene in the maturity parameter formula possibly due to a variable degree of alkylation. Dealkylation of methylphenanthrenes to form parent phenanthrene occurs much earlier than of 1.35% reported in the literature. The increment of MPR and MDR values with maturity levels is mainly caused by different generation rates with a higher generation rate of thermally stable isomer than thermally unstable counterpart rather than isomerization between them. Caution should be taken when empirical formula published in literature based on commonly used maturity parameters is directly applied for maturity estimation as no universal applicable correlation is likely available.
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    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
    (2021-06) Wang, Qianru; Larter, Steve; Huang, Haiping; Snowdon, Lloyd; Oldenburg, Thomas; Dong, Mingzhe; Fowler, Martin
    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.