Combining Rock-Eval pyrolysis and organic petrographic techniques to study the organic facies of the Pabdeh Formation in the Rag-e-Sefid Oilfield, SW Iran

In this study, the organic facies and depositional environments of the Pabdeh Formation are investigated in the Rag-e-Sefid Oilfield located in the southern Dezful Embayment. Little information exists about the organic facies properties of this source rock in the Zagros basin. In the present study, a total of 4 cutting samples were collected from well No. 99 of the Rag-e-Sefid Oilfield. These samples are characterized by a combination of Rock-Eval pyrolysis and organic petrographic techniques. Based on the diagrams of Tmax versus HI, the studied samples contain type II/III kerogen with thermal maturity corresponding to the early stages of the oil generation window. Organic petrographic results are consistent with the presence of a highly organic-rich zone in the middle parts of the Pabdeh Formation, while the upper and lower parts are poor in organic matter. The organic-rich part of the Pabdeh Formation contains abundant amorphous organic matter, bituminite, and framboidal pyrite typical of anoxic depositional environment. The organic-poor sections on the other hand contain negligible organic matter with euhedral secondary pyrite in a light-colored matrix, which suggests oxic depositional condition. These observations suggest that different parts of the Pabdeh Formation were deposited under different environmental conditions. Only the middle part of the Pabdeh Formation has considerable potential for hydrocarbon generation.