Geochemical characteristics of Bangestan Reservoir in one of the S.W. Iranian Oilfield

Organic geochemistry is admitted as a potential approach for hydrocarbon system analysis. This study provides a typical example from detailed geochemical analysis on oil samples taken from Sarvak and Ilam carbonate reservoirs within a giant oilfield in Dezful embayment, southwest Iran. Bulk oil composition data suggest significant differences between the oil samples, especially, in terms of API and Saturate/Aromatic ratio. This was further confirmed based on the results of Gas Chromatography (GC), Gas Chromatography-Mass Spectrometry (GC-MS), and Detailed Hydrocarbon Analysis (DHA). On the other hand, based on the derived biomarker data, Sarvak and Ilam reservoirs were most probably charged from a dominantly shale and carbonate source rock, respectively, deposited within an open marine source rock including kerogen type II. Moreover, oil samples taken from Sarvak reservoir shows a considerably higher thermal maturity than the ones collected from Ilam reservoir that could be due to the differences in source rock formation or its facies. This condition can be explained based on the observed high to moderate concentration of Olenane/C۳۰H ratio in Ilam oil samples that suggest contribution of carbonate-rich Pabdeh formation as a source rock. However, another possible scenario is regional variation in lithological facies of Kazhdomi formation.