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Abstract

A reservoir geochemical study in the Gullfaks field and its surroundings fields was performed to detect compositional differences in petroleum, from different reservoirs and sectors, which may be related to its complex filling history. The molecular composition of hetero- and polycyclic aromatic hydrocarbons, C7 hydrocarbons together with δ13C data indicate that oils from the Gullfaks South field derived mainly from more terrestrially-dominated source facies, whereas oils from the Gullfaks and Gullfaks West fields sourced mainly from marine algal material. Although, the oil sample from the Gullfaks West field has the lightest δ13C values of n-alkanes and isoprenoids, petroleum from the Brent Group and the Cook Fm. reservoirs in the Gullfaks field were not distinguished isotopically in spite of having been filled from different source basins. In contrast, hetero- and polycyclic aromatic hydrocarbons as well as light hydrocarbons allowed discriminating oil populations into the Gullfaks field, which were not differentiated using biomarkers and δ13C data. Here, the δ13C values of Pr and Ph coupled with molecular data of heterocyclic aromatic hydrocarbons and light hydrocarbons were very useful to discriminate oils from the Gullfaks area, whose compositions are more associated with source facies and depositional environment variations into Upper Jurassic source rocks.