Distribution and geochemical composition of oil-bearing fluid inclusions compared to crude oil, oil shows and rock extracts in a Campos Basin well, offshore Brazil

Carlos Eduardo Silva Coelho, Simon C. George, Herbert Volk, Peter Eadington, Andrew S Ross

    Research output: Contribution to journalArticle

    Abstract

    An offshore well containing a shallow, biodegraded producible oil zone underlain by an intermediate oil show zone (slightly biodegraded) and a deep oil show (unbiodegraded). The objective of this study was to screen for the presence of oil-bearing fluid inclusions (FIs), use this information for determining the extent of paleo-oil zones and compare their geochemistry to oils, oil shows and rock extracts. A Grains with Oil Inclusions (GOITM) value of 5.3% in the producible oil zone is moderate but FIs are small (< 5 µm) and rare. Lower GOI values (0.7-2.0%) in the intermediate oil show interval are evidence for migration and possibly accumulation of oil. In the deep oil show FIs occur more frequently (GOI = 9.6-19%), are larger and are more abundant within grains. Their geochemical signature is similar to the oil show in terms of secondary alteration (non-biodegraded), maturity (peak of oil window) and source signature (clay-rich, probably Cretaceous or younger, suboxic marine shales). The inclusion oil does not correlate with the less mature and lacustrine producible oil or the intermediate oil show, nor does it correlates with the significantly less mature marine mudstones in the well. Similar maturities (peak of oil window) are indicated by parameters calculated from a wide boiling range of compounds, so PIs probably trapped oil from a single charge event. Both palaeo- and current oil in the deep oil show interval differ from the upper producible oil and we infer that they were generated from a deeper source and migrated vertically
    Original languageEnglish
    Pages (from-to)19-38
    Number of pages20
    JournalRevista Brasileira de Geociencias
    Volume38
    Issue numberSuppl. 1
    Publication statusPublished - 2008

    Keywords

    • petroleum inclusions
    • crude oil
    • grains with oil inclusions
    • molecular composition
    • geochemistry

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