The late Permian succession of the Upper Indus Basin in northeastern Pakistan is represented by the carbonate-dominated Zaluch Group,which consists of the Arab,Wargal and Chhidru formations,which accumulated on the southwestern shelf of the Paleo-Tethys Ocean,north of the hydrocarbon-producing Permian strata of the Arabian Peninsula.The reservoir properties of the mixed clastic-carbonate Chhidru Formation (CFm) are evaluated based on petrography,using scanning electron microscopy (SEM),energy dispersive x-ray spectroscopy (EDX) and x-ray diffraction (XRD)techniques.The diagenetic features are recognized,ranging from marine (isopachous fibrous calcite,micrite),through meteoric (blocky calcite-Ⅰ,neomorphism and dissolution) to burial (poikilotopic cement,blocky calcite-Ⅱ-Ⅲ,fractures,fracture-filling,and stylolites).Major porosity types include fracture and moldic,while inter-and intra-particle porosities also exist.Observed visual porosity ranges from 1.5-7.14％ with an average of 5.15％.The sandstone facies (CMF-4) has the highest average porosity of 10.7％,whereas the siticiclastic grainstone microfacies (CMF-3) shows an average porosity of 5.3％.The siliciclastic mudstone microfacies (CMF-1) and siliciclastic wacke-packestone microfacies (CMF-2) show the lowest porosities of 4.8％ and 5.0％,respectively.Diagenetic processes like cementation,neomorphism,stylolitization and compaction have reduced the primary porosities;however,processes of dissolution and fracturing have produced secondary porosity.On average,the CFm in the Nammal Gorge,Salt Range shows promise and at Gula Khel Gorge,Trans-Indus,the lowest porosity.