--> Abstract: A New Dimension in Chemostratigraphic Resolution Using Diterpane Biomarkers, by M. J. Moldowan, J. Dahl, D. Zinniker, S. M. Barbanti, and M. R. Mello; #90933 (1998).

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Abstract: A New Dimension in Chemostratigraphic Resolution Using Diterpane Biomarkers

Moldowan, J. Michael; Jeremy Dahl and David Zinniker - Stanford University; Silvana M. Barbanti and Marcio R. Mello - Petrobras/Cenpes

A diverse array of diterpenoid biomarkers are biosynthesized by land plants. The resulting diterpanes found in petroleum and rock extracts provide a complex fingerprint similar to micropaleontological diversity. Because diterpanes are often in low abundance in petroleum, we have developed new methods to analyze them based on zeolites and metastable reaction monitoring-gas chromatography-mass spectrometry (MRM-GC-MS) or GC-MS-MS. Diterpane fingerprints can be used to distinguish between subtly different source rocks, or between oils generated from the same source rock, but emanating from neighboring petroleum kitchens. The resolution gained from diterpane analysis of oils can provide the foundation data for mapping petroleum migration in basins with multiple source kitchens or multiple source-rock intervals and ages.

Diterpane biomarkers are usually associated with higher plant input to a source rock or oil. Geochemical studies in S. E. Asia and Australia have taken advantage of such compounds in correlation and oils fingerprinting. However, diterpanes have found little application thus far in Latin America. This study demonstrates the wide diversity of these compounds in the oils of the Tertiary and Upper Cretaceous systems in Northern South America and their potential use to distinguish very similar oils generated from the same source rock, but from different locations.

A world-wide collection of oils from Tertiary and Cretaceous petroleum systems across the northern part of South America have been analyzed for diterpanes and bicadinanes by GC-MS-MS and (MRM)-GC-MS methods, sometimes assisted by concentration enhancement using zeolites. The tricyclic diterpanes rimuane and isopimarane can be found in most oils and rock extracts of those source ages. However, the bridged tetracyclic diterpanes phyllocladane and kaurane were less frequently encountered. An isomer of fichtelite was identified using standards as being an abundant diterpane in some Tertiary oils. Bicadinanes are sesqiterpene dimers often reported in S. E. Asian oils. They are generally encountered in Cretaceous and Tertiary oils, but usually in higher abundance in the Tertiary oils derived from terrestrial organic matter (Fig. 1).

Fingerprints and graphical displays of various diterpane ratios were seen to vary in a regional sense highlighting different locations (kitchens) where source rocks of the same age have generated. These data could be used to constrain regional oil migration maps for eventual use in basin modeling.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil