Investigation of the hydrocarbon potential and organic matter properties of the Sarcheshmeh Formation (Lower Cretaceous) in the eastern part of the Kopet Dagh Basin, NE Iran

In the Kopet Dagh Basin (NE Iran), as a known hydrocarbon province, marls, argillaceous limestones, and limestones of the Lower Cretaceous Sarcheshmeh formation can be considered as the possible source rock. Although, less geochemical data related to the source rock evaluations are available from these marine sediments. The present study evaluates the organic geochemical properties and the hydrocarbon generation potential of the Sarcheshmeh Formation outcrop (Khomari section) in the eastern part of the basin. A total of ۲۰ outcrop samples were analyzed by organic geochemical and petrographic investigations (Rock-Eval pyrolysis, vitrinite reflectance measurements, and visual kerogen typing) to characterize the content, type, and thermal maturity of the organic matter. This study shows that Rock-Eval pyrolysis and microscopical techniques to achieve the main objectives of the present study are in good agreement with each other. The TOC and S۲ values of the studied samples are very low, and concluded that this formation does not have enough potential for hydrocarbon generation. Rock-Eval Hydrogen Index values (HI: ranging from ۵ to ۲۴۰ mg HC/g TOC) and visual kerogen analysis suggest that organic materials are predominantly composed of Type IV kerogen with some Type III. The average values of vitrinite reflectance (Ro: ۱.۱۶-۱.۳۱%) and Spore Coloration Index values (SCI: ۷-۸.۵) indicate that organic matter in analyzed samples is thermally mature. Consequently, Sarcheshmeh Formation may not be accepted as a source rock in the study area. However, the basin's Lower Cretaceous marine deposits, like Sarcheshmeh Formation, are still worth exploring for hydrocarbons because all studied samples were collected from outcrops and not from the deeper parts of the basin. Moreover, these sedimentary units in the western parts of the Kopet Dagh have a significant thickness; therefore, it is possible to find out more encouraging source rock geochemical results in the Sarcheshmeh Formation

Keywords:

Source rock potential , Rock-Eval pyrolysis , Organic petrography , Sarcheshmeh Formation , Kopet Dagh Basin.