Burial history reconstruction and thermal maturity modeling for the Middle Cretaceous-Early Miocene Petroleum System, southern Dezful Embayment, SW Iran

The Middle Cretaceous-Early Miocene Petroleum System is the most important hydrocarbon system in the Zagros Basin. Rock-Eval pyrolysis, organic petrography and thermal 1D modeling were performed on wells located in the southern Dezful Embayment. The results provide information on organic matter quantity and quality as well as burial and thermal histories of source rocks in the framework of the basin evolution. A total of 98 cutting samples from BK-4, KK-1, SI-4 and RS-2 wells were pyrolyzed by Rock-Eval 6. Also thermal maturity of organic matter derived from Tmax of Rock-Eval was interpreted in conjunction with vitrinite reflectance data (50 samples). The TOC values of the sequences mainly range from 0.5 to 2.5 wt.%. The average values of Tmax and vitrinite reflectance indicate that samples from the wells have reached maturities corresponding to early/mid oil generation. Reconstruction of thermal history suggests that various steady heat flow values (62, 54, 50 and 56 mW/m2 for BK-4, KK-1, SI-4 and RS-2 wells, respectively) resulted in the best fit between the calculated and the observed vitrinite reflectance and bottom hole temperatures in our modeling. Thus, values of heat flow decrease from 60 mW/m2 in the southern basin margin to about 50 mW/m2 along the NE of the Dezful Embayment and the Zagros Basin. According to our modeling results, the onset of oil generation from source rocks in the studied area occurs well after deposition of the seal rock and formation of traps, ensuring entrapment and preservation of migrated hydrocarbons.