OIL-OIL CORRELATION OF ASMARI AND BANGESTAN RESERVOIRS USING GAS CHROMATOGRAPHY AND STABLE ISOTOPES IN MARUN OILFIELD, SW IRAN*

Document Type: Regular Paper

Authors

1 Department of Geology, Faculty of Science, University of Shahid Chamran, Ahvaz, I. R. of Iran,

2 Department of Geology, Faculty of Earth Science, University of Shahid Beheshti, Tehran, I. R. of Iran

3 Department of Geology, Faculty of Science, University of Shahid Chamran, Ahvaz, I. R. of Iran

Abstract

For this study, Asmari (Oligo-Miocene) and Bangestan (Cretaceous) reservoir oils from the
Marun oilfield were studied geochemically. Gas chromatograms and stable isotopes of carbon and sulfur in
different oil fractions were studied. Normal alkanes nC15
+ are as high as 93% with a saturate percentage up to
53.9% which reveal a high maturity of Asmari and Bangestan reservoir paraffinic oils. Carbon Preference
Index of both reservoir oils are around one, indicating mature oil samples. Pr/nC17 and Ph/nC18 ratios have
confirmed this conclusion. The Pr/Ph ratio is less than one and the plot of δ13CAro.(‰) versus δ13CSat.(‰) both
indicate a marine reducing environment during the deposition of their source rocks. The organic matter
deposited in these sediments is of kerogen Type II (Algal). Stable carbon isotope results versus Pr/Ph ratio
indicate that both oils originate from the same shaley limestone of the Mesozoic age. This study also proves
that H2S gas polluted Asmari oils have a similar isotopic range as Bangestan reservoir oil, hence the source of
contamination must have originated from the Bangestan reservoir. Isotopic and geochemical results, for the
first time, introduce three oil families; two H2S polluted families and one non-H2S polluted oil family; in the
entire Marun oilfield.

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