Upper Jurassic-Lower Cretaceous Source-Rock Evaluation and Oil—Source Rock Correlation in the Abadan Plain, Southwest Iran

Abstract

Eight oil samples from Lower Cretaceous Fahliyan reservoirs and 51 core and cutting samples from Upper Jurassic-Lower Cretaceous Garau Formation in Abadan Plain, Southern Iran, were analyzed using bulk property and molecular methods in order to identify their geochemical characteristics such as maturity and source depositional environment, as well as to correlate them to respective source rock(s). Rock-Eval pyrolysis and vitrinite reflectance measurements indicated that the Garau Formation, classified as a good-to-excellent source rock, the kerogen is mainly of Type II and the maturity is in peak oil generation. The crude oils of the Fahliyan reservoir are classified as light oil (API more than 35), non-biodegraded, saturate fraction, slight even/odd predominance, and front-end biased distribution in gas chromatogram. According to molecular and isotopic data, the oils were generated by a marine carbonate source rock which was deposited under the anoxic condition. Furthermore, all the studied samples reveal compositional similarity and hence can be assigned to one oil family, originating from a common source rock. Based on compositional similarities of biomarkers and isotope data in the studied crude oils and source rock, the Upper Jurassic-Lower Cretaceous Garau Formation can be regarded as the main source rock of the oils.