Geochemical investigation of oils from Cretaceous to Eocene sedimentary sequences of the Abadan Plain, Southwest Iran

Oil samples from Lower Cretaceous to Eocene reservoirs in southwest Iran were analyzed using gas chromatography-mass spectrometry and gas chromatography-isotope ratio mass spectrometry for genetic classification of oil families and determining their maturity. The Studied oil samples are non-biodegraded and their gravity range from 18.3 to 37 degrees API. The slight even/odd n-alkane predominance, coupled with low Pr/Ph values, suggests their likely source rocks with a predominance of algal organic matter, type IIS kerogen deposited under strongly reducing marine environments. The biomarker distribution of investigated oils is characterized by high concentration of both C-29 and C-30 hopanes and ratios of C-29/C30H are generally greater than unity. There is a marked predominance of C-29 regular sterane over C-27 and C-29 homologs in our studied oils. High sterane/hopane values and cross plot of the delta C-13 sat versus delta C-13 aro show contribution of marine organic matter. Medium value of gammacerane index and other salinity indices show water density stratification and high salinity conditions of the environment of deposition. It can be concluded that the studied reservoirs, due to their variable maturity have different API gravity and contain two oil families (types A and B) with latter being deeper and comprising more mature oils. (C) 2015 Elsevier Ltd. All rights reserved.