Organic Geochemical Characteristics of the Cretaceous Source Rocks and Crude Oils, Iranian Sector of the Persian Gulf

This study tries to assess the potentiality of the Cretaceous source rocks deposited in the Iranian sector of the Persian Gulf and investigates their possible relationships with the generated hydrocarbons in the study area. Rock-Eval pyrolysis, stable carbon isotope composition, biomarker analysis and vitrinite reflectance are used to characterize 250 cutting samples of the Cretaceous Kazhdumi Formation, Ahmadi Member of the Sarvak Formation and Gurpi Formation in 18 fields. A fair source rock potential is suggested for the Kazhdumi and Gurpi formations while, a fair to good source rock characteristics is found for the Ahmadi Member. Several maturity indicators show that the Kazhdumi Formation and the Ahmadi Member entered the main oil window but, the Gurpi Formation is immature to early mature in the study area. Bulk properties, biomarker parameters and stable carbon isotopic composition of crude oil samples from Jurassic and Cretaceous reservoirs in the study area discriminate two distinct groups between the crude oil samples. Group-I oils were probably derived from Cretaceous source rocks and Group-II oils from Late Paleozoic to Early Jurassic source rocks. Correlation studies between the studied crude oils and source rock introduces the Ahmadi Member as a probable source rock for the Group-I oils.