A study of reservoir potential of Cretaceous–Paleocene successions of Nizampur basin, Khyber Pakhtunkhwa, Pakistan: constraints from fracture analysis, petrography and geochemistry

The current work deals with comparative study of reservoirs potential of best exposed Cretaceous–Paleocene successions in Nizampur Basin, Khyber Pakhtunkhwa, Pakistan. Outcrop fractures data were collected, integrated and compared with the petrography, scanning electron microscope (SEM) and energy dispersive X-ray analysis (EDX) data of selected samples. These fractures data include orientation, attitude (Dip/Strike), fracture density (F.D), frequency and their distribution. The methodology adopted comprises of fracture data by scanline circle inventory method (CIM) and statistical calculations for porosity and permeability by Monte Carlo equation. The data were collected from three stations with 119 circles inventories. Moreover, the natural fracture reservoir system (NFR) was used to classify the reservoir potential based on calculated the results. The analyzed formations show intermediate to low porosity and permeability and classified as Type-2 or Types-3 established on the data from petrography/SEM/EDX and outcrop fractures data, respectively. The results further displays that, the fractures provide essential permeability only in case of Types-2 while in case of Type-3 the fractures provide a permeability assistance. The limestone interbeded with glauconitic sandstone in the lower most part of the Lumshiwal Formation may act as prolific reservoir intervals sealed by sandy carbonaceous shale within this unit. Overall, the depositional environment and digenetic processes mainly controlled the reservoir potential but in general, the Cretaceous–Paleocene successions may be considered as good reservoirs for holding and transmitting hydrocarbons.