Geochemical evaluation of the Sarvak and Fahliyan reservoirs crude oils by biomarker data in one of the Abadan Plain oilfields

In this study, 8 crude oil samples of the Sarvak (5 samples) and Fahliyan (3 samples) reservoirs from one of the main oilfields of the Abadan Plain was assessed geochemically by Liquid Chromatography, Gas Chromatography (GC) and Gas Chromatography Mass Spectrometry (GC-MS) techniques. Types of crude oils of the Sarvak reservoir are Paraffinic Naphtenic and Aromatic Intermediate and are Paraffinic type for the Fahliyan reservoir crude oils. Biomarker ratios of saturate fractions such as variation of Pr/nC17 and Ph/nC18 ratios and Pr/Ph versus C27/C29 (20R) Sterane diagram indicate formation of source rock in reducing marine environment for both oil reservoirs. Furthermore, high amount of C29 Sterane in compare to C27 and C28 Steranes show that organic matter of source rock was formed in marine environment with terrestrial kerogen input. High amount C29 Hopane versus C30 Hopane, variation C27 (Dia/Dia䗨) Steranes versus Pr/(Pr), low amount of Diasteranes versus Steranes and variation Sterane/Hopane versus C27/C29 Steranes show carbonate- shale lithology for source rock of studied oils. Depending on high amount of resin, scattering of normal alkanes, high values of Pr/nC17 and Ph/nC18 and higher UCM in compare to other samples, K11 and K15 samples of the Fahliyan reservoir and B5 sample of the Sarvak reservoir demonstrate slight to moderate biodegradation while B19 sample show very slight biodegradation. According to variation of Pr/nC17 vs. Ph/nC18, C29 Sterane 20S/(20S�) vs. C32 Hopane 22S/(22S�), C29 Sterane 20S/(20S�) vs. C29 Sterane αββ/(αββααα) samples from both reservoirs denote early oil window formation. Samples from the Fahliyan reservoir have high thermal maturity in compare to the Sarvak reservoir samples.