Organic Geochemical Characteristic Of Crude Oils From Orange Graben, South Sumatra Basin

Lemat Formation in the Orange Graben in the South Sumatra basin has been considered as syn-rift sediments consist of fluvio-lacustrine sediments, create source rock with fluvio-lacustrine characterize. Based on existing publications, showing that the oils from Orange Graben have fluvio-deltaic characterization and generated by source rock from Talangakar Formation with fluvio-deltaic depositional environment. This paper emphasizes geochemistry methods. Source rock analysis, consist of 26 samples for carbon isotope and 14 samples for biomarker, while oil analysis, consist of 15 samples for carbon isotope and 19 samples for biomarker. Characterization has been based on qualitative and quantitative data. Qualitative data comprise evaluation based on chromatograms and mass-fragmentograms, whereas quantitative data consists of a series of cross-plots, eg. cross plot of carbon isotope δ13C saturates - aromatics, distribution of C27-C28-C29 sterane, Pr/nC17-Ph/nC18, Pr/Ph-Pr/nC17, carbon isotope δ13C saturates-Pr/Ph, Pr/Ph-total hopane/total sterane, and ratio of C26/C25 (tricyclic). Based on geochemical result of analysis, source rocks of Lemat Formation in the Orange Graben interpret as source rock with fluvio-deltaic characterize, have terrestrial influence while Talangakar Formation in the Orange Graben interpreted as source rock with deltaic characterization, having marine and terrestrial influence. Both of them , consist of humic kerogen. Whereas, oil samples in the Orange Graben interpreted as oilwhich is generated by source rock with fluvio-deltaic characterization, having terrestrial influence, in anoxic-suboxic-oxic conditions, consisting of humic kerogen. Correlation result between source rocks and oils in the Orange Graben, indicating that fluvio-deltaic oil type in the Orange Graben are correlate with not only the source rocks of Talangakar Formations but also with source rock of Lemat Formation.