OIL-OIL CORRELATION OF ASMARI AND BANGESTAN RESERVOIRS USING GAS CHROMATOGRAPHY AND STABLE ISOTOPES

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