Potential Evaluation and Basin Modeling of the Pabdeh Formation in Zagros Basin: A Case Study

Abstract

Pabdeh Formation is one of the most important source rocks in Zagros basin. In this study, thermal modeling and comparing of hydrocarbon potential evaluation of Pabdeh Formation in Mish Anticline and Gachsaran oil field have been investigated. For this reason, Rock-Eval pyrolysis was carried out on 21 cuttings samples collected from 2 boreholes (Well No. 55 and 83) of Gachsaran oil field and outcrop of Mish anticline. Accordingly, the Kerogen types of Pabdeh Formation in Gachsaran oil field are II, but in Mish anticline are type II and III. The amount of inert organic carbon determined for the Pabdeh Formation in Mish anticline is about 4.879 wt%, while for Gachsaran oil field, it is estimated at 0.153 (Well. No. 55) and 1.156 (Well. No. 83) wt%. Absorption of hydrocarbon by rock matrix was also determined. The amount of absorption in Mish anticline is more than that of Gachsaran oil field. This is mostly due to the presence of argillaceous matrix in this area, but the clays have not been successful in absorbing organic matter; this is due to the result obtained from small amount of organic matter in the basin. The Rock-Eval data revealed that the sedimentary paleo-environment strongly affected the source potential of this formation as it changed from the continental and Deltaic in the Mish anticline to deeper marine in Gachsaran oil field. In addition, curves of Burial history were drawn for Gachsaran well No. 55, in order to assess the thermal maturity of the Pabdeh formation. The results of the methods indicated that Pabdeh formation in Gachsaran oil field had a good to very good hydrocarbon potential and had entered to oil window.