Basin and petroleum system modeling of the Cretaceous and Jurassic source rocks of the gas and oil reservoirs in Darquain field, south west Iran

In south west Iran, in the Abadan Plain, there are several giant gas and oil reserves in Jurassic and Cretaceous carbonates, such as Darquain, where there are excellent source rocks in the Early Cretaceous and Jurassic successions. In present study, petroleum generation and migration from these source rocks were evaluated. Maturity state of organic matter was determined with Organic petrography and results were used for calibration of thermal model. Basin modeling was used for investigation of petroleum generation and migration history. Burial history and 3D thermal model were constructed for the study area using Temis suite and Genex software. Modeling shows source rocks of Jurassic, such as Sargelu and Neyriz are in gas maturity state, oil generation phase passed before Cenozoic. It appears that gas from Jurassic source rocks accumulated in Najmeh and did not reach to Cretaceous Fahliyan reservoir. Cretaceous reservoir in Fahliyan Formation has been charged by the Garau Formation. This source rock reached to oil window in Early Cretaceous time and began hydrocarbon expulsion at the end of Cretaceous when the Darquain structure formed. Migration paths of hydrocarbons shifted from NE to SW direction about 11 Ma in response to changes in regional structural dip contemporary with the Zagros Orogeny. Modeling results indicate that the quantity of gas and oil generated in the kitchen area was more than the reservoirs' capacity. Therefore, the surplus hydrocarbon could have migrated laterally out of reservoir area.