Source Rock Evaluation of Patala & Chichali Formations, Upper Indus Basin, Pakistan, Based On Available Data

Abstract

Organic carbon content, of most of the samples of Chichali shales, studied in the southern Hazara area, probably once represented very well to excellent source potential, because the current extraordinarily very low values for S1, S2, and S3, Genetic Potential (GP), Hydrogen Index (HI), and Oxygen Index (OI), clearly indicates that Chichali Shales, in the study area are at present spent source rock. Oil and gas generated, during the course of thermal maturation of Chichali shales, might have migrated and accumulated within the potential traps of the overlying and adjacent areas. Organic-petrographic studies of samples of Patala Formation from main Salt Range show that samples are immature whereas samples from Kohat and central Potwar area are mature and samples from western Salt Range are slightly less mature than the samples from Kohat and central Potwar area. Though Infra-Cambrian Salt Range Formation and Eocene Jatta Jypsum exhibit excellent source potential, but on the basis of available information, it can be concluded that the late Paleocene to early Eocene Patala Formation of the Potwar Basin represents a source facies which is very similar to one which has generated the oil in Potwar sub-basin. The extracts from samples have a geochemically close affinity to the Potwar oil. Thus, it can be inferred that the Patala Formation is the actual source formation which has generated the oil present in different stratigraphic levels in the Potwar Depression. Most probably, the source facies was developed in the central, northern, western Potwar, and in Kohat area. The source material is interpreted as amorphous, partly terrestrial, which is deposited in slightly reducing conditions.