Abstract:
The detailed microfacies analysis carried out for stratigraphic section of Chorgali Formation located at Bochaal Kalan in the eastern part of Salt Range. Limestone of Chorgali Formation is planner to nodular and is interbedded with shales. The limestone is highly fractured. Based on petrographic and field studies two microfacies have been identified. 1) bioclastic mudstone – wackestone 2) bioclastic wackestone. Subtidal facies described by the common occurrence of benthic foraminifera and the presence of echinoderms. Integration of well log data as well as petrographic data from the outcrop samples suggest that the formation has been inferred to be deposited in shallow marine subtidal shelf carbonate type of environment in this area. The diagenetic studies shows that the formation undergone compaction, fractures fill with calcite cement, neomorphism and micritization. Faunal assemblage includes smaller Rotaliidae, Lockhartia, Miliolid, Soritidae, peloids, ostracods, planktons, echinoderms and textularia. The average porosity of 54.40 meters thick Chorgali Formation in Turkwal Deep-01 is 9 % whereas the average effective porosity is 6 %. Similarly the thickness of Chorgali Formation in Balkassar-OXY-01 is 45.72 meters with average porosity of 11% and average effective porosity of 8%.The average porosity and permeability of seven meters thick exposed stratigraphic sequence is 3.92% and 0.244 md respectively. In both of the above mentioned wells porosity is highly variable from zone to zone but cannot produce sufficient amount of hydrocarbon due to very low effective porosity in probable reservoir zones. Although porosity and permeability of the outcrop samples is quite low due to diagenetic processes of cementation, compaction, neomorphism and micritization, but fracturing due to later tectonic deformation enhance the permeability in some cases.
