Hydrocarbon Source Rock Evaluation of the Super Giant Ahwaz Oil Field, SW Iran

Dezful Embayment in Southwest of Iran is one of the most potential areas for exploration and development of the hydrocarbon reservoirs in the word. This zone includes some super giant oil fields likes Ahwaz, Maroun, Gachsaran, Agha Jari and some other oil fields. Several potential source rock units with different geological ages were deposited in this tectonically developed depression making this area as the most prolific region in the Middle East. The most important source rocks in the Dezful Embayment are the Lower Paleocene-Eocene Pabdeh Formation, the Santonian-Masstrichtian Gurpi Formation, the Albian Kazhdomi Formation and the Neocomian-Aptian Gadvan Formation. The contribution of each source rock to the charge of the Dezful Embayment oil fields was extremely variable. Source rock maturity and potential of these source formations at the Ahwaz oil field in the SW of Iran have been investigated by Rock Eval 6. The petroleum generating potential of these source rocks was evaluated by different parameters including Tmax, TOC, S1, S2, HI, OI, and PI. According to these parameters the Albian Kazhdumi and the Lower Paleocene-Eocenee Pabdeh Formations have the highest potential for hydrocarbon generation and assumed to have charged the Asmari and Bangestan reservoirs in the Ahwaz oil field. The Rock-Eval parameters suggest that the Gadvan and Gurpi Formations are the subordinate source rocks in this area and their contribution to the charge of the reservoirs is negligible.Burial and thermal history modeling was performed to determine timing of hydrocarbon generation in the Pabdeh and Kazhdumi source rock in the Ahwaz oil field. Burial history reconstruction and thermal modeling indicate that beginning of the oil window was dated as 15Ma for the Kazhdumi Formation and 5Ma for the Pabdeh Formation. The beginning of the oil window occurred for the two source rocks when they were buried to a depth of 3500m. The expulsion of oil would have begun 10 Ma ago for the Kazhdomi Formation and 3 Ma for the Pabdeh Formation. The main phase of Zagros folding occurred during the late Miocene and Pliocene. The migration of hydrocarbons from source rocks, was enhanced by the syn-orogenic fracturing of reservoir rocks in the Asmari and Bangestan (Sarvak and Illam) Formations