Organic geochemistry of Gadvan and Kazhdumi formations (Cretaceous) in South Pars field, Persian Gulf, Iran

In Southern Iran, Gadvan (Barremian-early Aptian) and Kazhdumi (Albian) formations are the most effective source rocks and have produced the majority of hydrocarbons reserved in the Zagros Basin especially in Dezful Embayment and Persian Gulf area. In this article, hydrocarbon potential of Gadvan and Kazhdumi formations is investigated in the South Pars field which is southern extension of the North field of Qatar Country. This field is located in Persian Gulf waters and is actually the northern extension of Qatar Arc Paleohigh where geological history of Gadvan and Kazhdumi formations is different from nearby area regarding depositional setting, burial history and source rock maturity.In this study, Gadvan and Kazhdumi formations as source rock candidates, which underlay Upper Dariyan and Mauddud members, respectively, were sampled in two drilled wells of the South Pars field for routine geochemical analysis to investigate hydrocarbon potential of these formations and source rock identification of trapped oil in the Upper Dariyan and Mauddud members. Several samples from top to the bottom of the formations were taken and analyzed by Rock-Eval pyrolysis. The average TOC content of Gadvan and Kazhdumi formations is 0.79 wt. % and 0.49 wt. %, respectively. Rock-Eval results (e.g. HI vs. Tmax) represent that TOC content of these formations contains type II-III kerogens which haven't suffered sufficient thermal maturity (Ro < 0.5%) in this study area. Moreover calculated S2/S3 ratio implies that these formations in central part of Qatar Arc, South Pars field couldn't produce noticeable liquid hydrocarbon.As it is believed, Gadvan and Kazhdumi formations to be source of trapped oil in the system, therefore, in the South Pars field reserved hydrocarbon in Upper Dariyan (Aptian) and Mauddud (late Albian) members which overlie Gadvan and Kazhdumi formations, respectively, are probably generated from Gadvan and Kazhdumi formations of the nearby through and flanks of the Qatar Arc where the burial depth and temperature increase then generated hydrocarbons in downdip area are migrated to the upper carbonate reservoirs in the crest part of the Qatar Arc. Long path migration of the hydrocarbon and source rock with lower organic matter are caused hydrocarbon accumulation in the South Pars Oil Layer (Al-Shaheen) which is approved by professional petrophysical and geological studies of the field.