Geological and geochemical conditions for the formation of the oil composition in the deposits of the Permian and Jurassic oil and gas complexes in the Fukang depression (Junggar basin)

Within the eastern part of the Fukang depression, the main productive series are confined to the Permian and Jurassic oil and gas complexes (OGC), in which the Middle Permian and Lower-Middle Jurassic oil and gas source rocks (OGSRs) are distinguished. The article discusses in detail the oil and gas source characteristics of the Middle Permian and Lower-Middle Jurassic rocks, the molecular composition of oils and bitumoids from the OGSRs, and also interprets the characteristics of the biomarkers in them from the standpoint of the sedimentary-migration theory of oil generation. An attempt is made to explain the reasons for the difference in the properties and composition of oils from different OGCs. It is shown that the composition of hydrocarbon fluids of deposits is determined not only by the geological and geochemical conditions of sedimentation of oil and gas source deposits, but also associated with migration processes and subsequent secondary changes in the accumulation. In terms of composition, three groups of oils were identified: Permian and Jurassic heavy oils with a light carbon isotopic composition and the presence of β-carotene and gammacerane, they underwent different degrees of biodegradation, which depended on the geological conditions of the deposits; Permian medium oils in density (0.84 and 0.87 g/cm3), the composition of biomarkers of which is very close to that of the first group, and Jurassic light oils with a high content of solid paraffins and a heavier carbon isotopic composition, almost do not contain β-carotene and gammacerane concentrations are low.

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New equation to decipher the relationship between carbon isotopic composition of methane and maturity of gas source rocks

Science China Earth Sciences ◽

10.1007/s11430-020-9692-1 ◽

2021 ◽

Vol 64 (3) ◽

pp. 470-493 ◽

Cited By ~ 1

Author(s):

Jianping Chen ◽

Xulong Wang ◽

Jianfa Chen ◽

Yunyan Ni ◽

Baoli Xiang ◽

...

Keyword(s):

Isotopic Composition ◽

Carbon Isotopic Composition ◽

Source Rocks ◽

Carbon Isotopic ◽

Gas Source ◽

New Equation ◽

The Relationship

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Hydrocarbon biomarkers and isotopic composition of carbon from bitumoids and oils of Mesozoic sediments in the western part of the Yenisei-Khatanga oil and gas region

Georesursy ◽

10.18599/grs.2019.1.47-63 ◽

2019 ◽

Vol 21 (1) ◽

pp. 47-63

Author(s):

Alexander P. Afanasenkov ◽

Tatyana P. Zheglova ◽

Alexander L. Petrov

Keyword(s):

Isotopic Composition ◽

Oil And Gas ◽

Carbon Isotopic Composition ◽

Source Rocks ◽

Type I ◽

Composition Distribution ◽

Carbon Isotopic ◽

Hydrocarbon Biomarkers ◽

Humus Type ◽

Hydrocarbon Deposits

Based on analyzes of carbon isotopic composition, distribution and composition of hydrocarbon biomarkers of oils and bitumoids from source rocks of the Mesozoic sediments in the western part of the Yenisei-Khatanga oil and gas region and the northeast of the West-Siberian plate, two groups of oils and bitumoids are identified, genetically associated with organic matter, mainly sapropel type (I group) and mainly humus type (II group). The genetic correlation of oils and bitumoids has been made. Possible foci of generation, which participated in the formation of hydrocarbon deposits, have been determined.

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Determination of carbon isotopic composition of individual light hydrocarbons evolved from pyrolysis of source rocks by using GC-IRMS

Chinese Science Bulletin ◽

10.1007/bf02893777 ◽

2000 ◽

Vol 45 (S1) ◽

pp. 7-10 ◽

Cited By ~ 1

Author(s):

Ansong Geng ◽

Yongqiang Xiong

Keyword(s):

Isotopic Composition ◽

Carbon Isotopic Composition ◽

Source Rocks ◽

Light Hydrocarbons ◽

Carbon Isotopic

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UNDERSTANDING SOURCE, DISTRIBUTION AND PRESERVATION OF AUSTRALIAN NATURAL GAS: A GEOCHEMICAL PERSPECTIVE

The APPEA Journal ◽

10.1071/aj00026 ◽

2001 ◽

Vol 41 (1) ◽

pp. 523 ◽

Cited By ~ 40

Author(s):

C.J. Boreham ◽

J.M. Hope ◽

B. Hartung-Kagi

Keyword(s):

Organic Matter ◽

Natural Gas ◽

Isotopic Composition ◽

Carbon Isotopic Composition ◽

Source Rocks ◽

Source Distribution ◽

Hydrocarbon Gases ◽

Carbon Isotopic ◽

Wet Gas ◽

Gaseous Hydrocarbons

Natural gases from all of Australia’s major gas provinces in the Adavale, Amadeus, Bass, Bonaparte, Bowen/ Surat, Browse, Canning, Carnarvon, Cooper/Eromanga, Duntroon, Gippsland, Otway and Perth basins have been examined using molecular and carbon isotopic compositions in order to define their source, maturity and secondary alteration processes.The molecular compositions of the gaseous hydrocarbons range from highly wet to extremely dry. On average, reservoired gases predominantly derived from land plants are slightly wetter than those derived from marine sources. The non-hydrocarbon gases CO2 and N2 were sourced from both inorganic and organic materials. A mantle and/or igneous origin is likely in the majority of gases with CO2 contents >5%. For gases with lower CO2 contents, an additional organic input, associated with hydrocarbon generation, is recognised where δ13C CO2 is A strong inter-dependency between source and maturity has been recognised from the carbon isotopic composition of individual gaseous hydrocarbons. This relationship has highlighted some shortcomings of common graphical tools for interpretation of carbon isotopic data. The combination of the carbon isotopic composition of gaseous hydrocarbons and the low molecular weight nalkanes in the accompanying oil allows our knowledge of oil-source correlations and oil families to be used to correlate gases with their sources. This approach has identified source rocks for gas ranging in age from the Ordovician in the Amadeus Basin to Late Cretaceous- Early Tertiary sources in the Bass and Gippsland basins. The carbon isotopic composition of organic matter, approximated using the δ13C of iso-butane, shows a progressive enrichment in 13C with decreasing source age, together with marine source rocks for gas being isotopically lighter than those from land plant sources. The Permian was a time when organic matter was enriched in 13C and isotopically uniform on a regional scale.Secondary, in-reservoir alteration has played a major role in the modification of Australian gas accumulations. Thus, biodegradation, prominent in the Bowen/Surat, Browse, Carnarvon and Gippsland basins, is found in both hydrocarbon and non-hydrocarbon gases. This is recognised by an increase in gas dryness, elevated isoalkane to n-alkane ratio, differential increase in δ13C of the individual wet gas components, a decrease in δ13C of methane and a reduction in CO2 content concomitant with enrichment in 13C. Evidence of water-washing has been identified in accumulations in the Bonaparte and Cooper/Eromanga basins, resulting in an increase in the wet gas content. Seal integrity is also a major risk for the preservation of natural gas accumulations, although its effect on gas composition is only evident in extreme cases, such as the Amadeus Basin, where preferential leakage of methane in the Palm Valley field has resulted in the residual methane becoming enriched in 13C.The greater mobility of gas within subsurface rocks can have a detrimental effect on oil composition whereby gas-stripping of light hydrocarbons is common amongst Australian oil accumulations. Alternatively, the availability of gas, derived from a source rock common to or different from oil, was likely to have been a prime factor controlling the regional distribution of oil, whereby mixing of both results in increased oil mobility and can lead to a greater access to the number and types of traps in the subsurface.

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