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Biomarker maturity parameters: The role of generation and thermal degradation

Lookup NU author(s): Dr Paul Farrimond


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The effects of burial maturation upon seven molecular maturity parameters, and the concentrations of individual biomarkers employed in these parameters, have been studied in a well in the Barents Sea. The depth interval between 1400 and 3000 m comprises homogenous Eocene claystones with effectively uniform organic carbon content (0.4-0.6%) and kerogen type (HI of 100-200 mg HC/g TOC). The quantitative biomarker data thus contain minimal interference from organic facies, hydrocarbon expulsion effects and the presence of migrated hydrocarbons Bulk geochemical data define the hydrocarbon generation threshold (or 'oil window') at around 2300 m. Molecular maturity parameters proceed to equilibrium, and in some cases demonstrate inversion at high maturity. These molecular changes are associated with major changes in biomarker concentrations. The %ββ hopane, %22S C31 αβ hopane and %20S C29 ααα sterane parameters proceed as a result of the balance between the relative rates of generation and thermal degradation of the different isomers. Increased concentrations of the individual isomers are interpreted to be the result of biomarker generation from the kerogen (mainly) and other macromolecular/polar fractions. The %αββ C29 sterane parameter and the three parameters involving rearranged hopanes (%Ts, %29Ts and %diahopane) operate at higher maturity levels, and proceed as a result of the relative rates of thermal degradation of the compound pairs. Isomerisation in the bitumen may also influence the operation of the parameters involving stereoisomers, but must be a relatively minor contribution.

Publication metadata

Author(s): Farrimond P, Taylor A, Telnaes N

Publication type: Conference Proceedings (inc. Abstract)

Publication status: Published

Conference Name: 18th International Meeting on Organic Geochemistry

Year of Conference: 1997

Pages: 1181-1197

ISSN: 0146-6380

Publisher: Organic Geochemistry: Pergamon


DOI: 10.1016/S0146-6380(98)00079-5