Geochemical characterization of the Fahlian, Gadvan, and Surmeh Formations in giant Gachsaran Oilfield

The aim of this study is geochemical evaluation of the Fahlian, Gadvan, and Surmeh formations as possible source rocks in Gachsaran oil field using Rock-Eval Pyrolysis manner. All of the studied samples possess migration index amounts lower than 1.5 showing indigenous nature of their hydrocarbons. TOC versus S2 and TOC against S1+S2 diagrams suggest fair hydrocarbon generation potential for the Fahlian and Surmeh formations and fair to good potential for the Gadvan formation. for the Fahlian and Surmeh formations type III kerogen and for the Gadvan formation mixed type II and II-III kerogens were identified. So, the Fahlian and Surmeh formations contain organic matter with terrigenous source (gas prone) and the Gadvan Formation possess both of marine and terrigenous organic matter (oil and gas prone). According to the cross plot of Tmax versus Hydrogen index (HI), the Gurpi formation is capable of mixed gas and oil, and gas generation and the Fahlian and Surmeh formations considered only gas prone formations. In terms of organic facies type, the surmeh, Fahlian, and Gurpi formations located in CD, C and CD, and BC and C zones of jones diagram, respectively. So, the Gadvan formation in compare to the Fahlian formation and the Fahlian formation in compare to the Surmeh formation, deposited under more anoxic conditions. In terms of thermal maturity, All of the Fahlian, Gadvan, and Surmeh formations located in oil window zone, but the Surmeh formation possess higher maturity than the Fahlian formation and the Fahlian formation have highr maturity in compare to the Gadvan formation.