Abstract
Early Cretaceous and Jurassic sequences in the southwestern Iran host some of the largest hydrocarbon reservoirs in the globe. This study is aimed at evaluating the maturity of hydrocarbon fluids, migration paths, and characteristics of Pabdeh, Kazhdumi, Garu and Sargelu source rocks in this region. For this purpose, 27 samples of Pabdeh and Kazhdumi Formations from wells in the northern part of Dezful Embayment were chemically evaluated by Rock–Eval pyrolysis. OpenFlow™ software was utilized to analyze the burial history, conduct 1D thermal modeling in four oilfields and perform 2D modeling on a section to estimate the maturity and extension of sediments. Results of the 1D modeling showed that the kerogens of Sargelu, Garu and Kazhdumi Formations were properly matured, leading to some hydrocarbon outflow, although the organic matter content of Pabdeh Formation was too immature to produce any hydrocarbon. Based on the plot of hydrogen index (HI) versus Tmax, it was found that the studied formations were dominated by type II kerogen and a mixed species of type II and type III kerogens. Results of the migration path modeling showed some leakage from the Kazhdumi Formation up to an overlying seal that prevented the hydrocarbons from seeping out to surface. The Early and Middle Cretaceous oil systems were found to be connected through geometrical features or faults, with the Kazhdumi Formation separating the two systems. The results further showed the migration of hydrocarbons, at a relatively high rate, into the Abadan Plate through the sub-Kazhdumi reservoirs.The Early and Middle Cretaceous petroleum systems were found to be connected through particular geometry features or possibly faults, with the two systems separated by Kazhdumi Formation. For most part, the intensity of the maturation processes was found to decrease from east to west of the study area.
Highlights
Southwestern Iran is among the richest hydrocarbon production areas in the world
This study aims at investigating the characteristics of rock units from Jurassic (Sargelu Formation), Cretaceous (Garu and Kazhdumi formations) and Paleocene–Oligocene (Pabdeh Formation) in the study area
1D modeling of wells located in Ab-Teymour, Band-e-Karkheh, East-Mushtaq and Ramshir fields in the north of Dezful Embayment was performed
Summary
Southwestern Iran is among the richest hydrocarbon production areas in the world. Extensive orogenic activity during the Miocene–Pliocene had formed the Zagros Mountains with two uplifts, one in the northern Lorestan and another one in the southern Fars (James and Wynd 1965).The study area was a structural subarea in the North Dezful just along the Zagros Fold-Thrust Belt. It is believed that most of Iran’s oil and gas is generated during the Jurassic (e.g. Sargelu Formation) and Cretaceous (Garu and Kazhdumi formations), with the generated hydrocarbons trapped in the reservoirs across the Dezful Embayment and Abadan Plain during the Cretaceous and Cenozoic (Kobraei et al 2019). Kazhdumi Formation is believed to have served the Dezful Embayment as the main source of hydrocarbon generation. This source rock has been dated back to Albian and hosts type II kerogen (Bordenave 2002; Versfelt 2001). Geochemical studies have revealed that the Pabdeh, Kazhdumi, Garu, and Sargelu Formations are the most important source rocks in the Zagros and Persian Gulf basins, feeding the reservoirs in different areas. On the border between the Abadan Plain and Dezful Embayment, there is much ambiguity in the process of hydrocarbon migration, leaving it yet to be clear that whether the oils of Ab-Teymour, Band-e-Karkheh and Susangerd fields have originated from a source rock within the Dezful Embayment or came from Abadan Plain
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