Facies analysis of the Chharat group and reservoir evaluation of the Nammal formation, salt range, upper Indus basin, Pakistan (T-1451) (MFN 8625)

Abstract

The present research work is dealt with early to middle EoceneChharatGroup and particularly, the Nammal Formation for detailed sedimen to logical investigations. Four stratigraphically important sections are investigated in the Salt Range, Upper Indus basin namely Nammal Gorge (NGS), Pail (PS), Sethi (SS) and BuchalKalan (BKS) sections from west to eastside of the Salt Range. Total 42 samples were thin-sectioned and microfacies study of Chharat Group with an in-depth investigation of the Nammal Formation in terms reservoir evaluation have been carried out. Based on estimated ratio of allochemical constituents and micrite, identifiedmicrofacis are; Foraminifera lime wackestone, Lime mud-wackestone, Foraminifera lime mudstone and Assilina rich lime wackestone at the NGS, Foraminifera lime wacke-packestone, Foraminifera lime wackestone and Bioclastic lime packestone at PS, Foraminifera lime wackestone and Bioclastic lime wacke-packestone at SS. Based on the relative abundance of biota, their associations and the presence of micritic matrix in various microfacies, the Namaml Formation is interpreted to be deposited in outer to mid and inner ramp settings. The Nammal Formation is largely affected and modified by different diagenetic events and the paragenetic sequence includes micritization, cementation, dissolution, neomorphism, pyritization, Partial dolomitization, mechanical compaction, stylolitization, fractures and veins formation. Of these, the fractures and dissolution on microscopic and macroscopic level are the dominant factors that enhance the reservoir potentiality of the Nammal Formation and the Nammal Formation has undergone through meteoric vadose to meteoric phreatic and passing through mixing zone and marine phreatic and eventually shallow and deep burial environments. The identified porosity types include intraparticle, vuggy, moldic, fenestral and fracture and the imageJ calculated porosities range from 4 to 6% and log estimated average effective or primary porosities are2 to 3% in range. The identified microfacies of the Sakesar Limestone include: Mixed lipoclastic lime wackestone, Larger foraminifera lime wackestone and Miliolid rich lime packestone at PS and microfacies of the Chorgali Formation are Bioclastic lime wacke-packestone, Foraminifera lime wackestone and Lime mud-wackestone at BKS. Based on faunal assemblage and micrite matrix the depositional environment of Sakesar and Chorgali formations are consistent with middle to inner ramp settings.