Microfacies Analysis and Reservoir Potential of Sakesar Limestone, Nammal Gorge (Western Salt Range), Upper Indus Basin, Pakistan

Abstract

The sedimentological study of the Lower Eocene Sakesar Limestone in Namal gorge section, Western Salt Range, was carried out to elaborate the microfacies, diagenetic settings and reservoir potential. The Sakesar Limestone is widely distributed across the Salt and Surghar ranges. It mainly consists of massive and nodular fractured limestone with subordinate marls and chert in the upper part. The Eocene succession is only comprised of conformable Sakesar Limestone and Nammal Formation in Nammal gorge. The detailed study was conducted after measuring the vertical thickness of 18m section and the 6 six samples were obtained symmetrically. To give the detailed insight of sedimentological characteristics the well cuttings of Sakesar Limestone from well Pindon-01, were studied along with the un-stained thin sections to investigate the microfacies, diagenesis and reservoir potential The well cuttings study revealed that the Sakesar Limestone is off white to dull grey calcite, moderately hard with cryptocrystalline to microcrystalline silica along with pyrite. Detailed field observations and laboratory investigations revealed that it contains Bioclastic wackstone microfacies. Neomorphism is present in various bioclasts. The presence of fractures filled with waxy leftover hydrocarbons makes it potential target for hydrocarbons. Petrophysical analysis shows an average hydrocarbon saturation of 85.5 percent in well Pindor-01 which confirms the huge reservoir potential of Sakesar Formation. Microfacies analysis indicates high lime mud and low faunal diversity which led towards the conclusion that the Eocene Sakesar Limestone was mainly deposited in semi restricted, low energy shallow marine shelf environment.