Burial and Thermal Histories Modeling for Sedimentary Basin Analysis of the Pabdeh Formation at One of the Oil Fields in the Southern Dezful Embayment

In this research, using one dimensional burial and thermal histories modeling, the effects of sedimentation, burial, subsidence and uplift on the temperature changes associated with depth and time and thus maturity of the organic matters in Pabdeh Formation have been studied. Three wells from one of the oil fields in the southern Dezful Embayment are involved in this investigation. The measured temperature and vitrinite reflectance have been used for the calibration of the models. The burial history diagrams show that the sedimentary basin had low sedimentation rate during the deposition of Pabdeh Formation in the Paleocene to Oligocene. This was associated with its low energy sedimentary environment at the passive margin of the Neo-Tethys. The highest rate of burial happened during the middle Miocene to middle Pliocene, associated with deposition of the Gachsaran, Mishan and Aghajari Formations in the Zagros Foreland Basin. Based on the thermal models, the Pabdeh Formation was exposed to the temperature higher than 60 °C in middle Miocene and reached to the 100 °C in the middle Pliocene, when the formation was in its highest burial depth. This situation was suitable for hydrocarbon generation; however, due to the main folding phase of the Zagros Orogeny from the middle Pliocene to present day, the uplift and erosions happened in the basin. This resulted in decreasing the temperature of the Pabdeh Formation and reducing the rate of organic matter maturity, and thus the hydrocarbon was not generated from the formation. According to low amount of vitrinite reflectance (Ro <0/6%), the Pabdeh Formation in the studied field is in the beginning of oil window and due to low amount of maturity, it can be considered as a high potential but immature source rock, which could not generate hydrocarbon.