Thermal History Reconstruction in the Soroosh and the Nowrooz Field, in the Persian Gulf, Based on Apatite Fission Track Analysis (AFTA) and Vitrinite Reflection (VR)

Bashari, Alireza, Iranian Offshore Oil Company, Tehran, Iran

Apatite Fission Track Analysis & Vitrinite Reflection, (AFTA& VR) data in the Soroosh­field are best interpreted in terms of the entire drilled sections of Quaternary to Cretaceous/Jurassic age being at maximum post-depositional temperatures, and maximum burial, at the present-day. This thermal history shows that any hydrocarbon source rocks at the Soroosh field are actively generating hydrocarbons at the present-day.

In contrast the AFTA and VR data in the Nowrooz- field are best interpreted in terms of a single Paleo-thermal episode, with the majority of the drilled section undergoing signifi­cant cooling that began at some time in the last 15 Ma, most likely between ~5 and 1 Ma ( Pliocene-Quaternary), due to uplift and erosion of ~1250m of previously deposited Agha Jari- Bakhtiari Formation. It follows that active source rock maturation at Nowrooz also ceased at this time.

Modelling of the hydrocarbon generation histories based on the AFTA-derived thermal histories, assuming a dominant Type III kerogen from possible Kahzdumi source rocks and a dominant Type III Kerogen for possible Kazdumi source rocks and a dominant type II kerogen for possible Fahliyan (Lower Ratawi Fm) source rocks, suggests that local sourcing of oil from the Kazhdumi Formation is unlikely. The most likely source rock for the Burgan reservoirs at Soroosh and Nowrooz is interpreted to be the Fahliyan Formation (Lower Ratawi Fm) Based on the available data. On the other hand, speculative modeling of Hendijan-1 well, down dip from Nowrooz field, does allow some oil to be generated from the Kazhdumi sequence at that location, and this might be available for migration to Nowrooz field.