Oleanenes in Niger Delta oils

摘要

Fifty-eight oils, from nine onshore and offshore oil fields in the present-day Niger Delta, were found to contain three oleanene isomers - olean-13(18)-ene, olean-12-ene and 18α-olean-12-ene. The geochemistry of the compounds reveals that the secondary isomers (olean-13(18)-ene and 18α-olean-12-ene) form during diagenesis from the precursor isomer (olean-12-ene). The presence of other angiosperm markers such as oleananes, the absence of measurable amounts of other olefins characteristic of immature organic matter, and the thermal maturity of the oils indicate that the oleanenes were inherited in the oil directly from the source rock and migrated from the source rock to the reservoir alongwith the oil.