Recognizing and classifying the naturally fractured reservoirs (NFRs) system for the cretaceous carbonate formation exposed along the Bagnotar-Baragali Section, north Pakistan: Implications from surface fractures, petrography and geochemistry

Abstract The current work deals with the classification of NRFs system for reservoirs characterization of Cretaceous Kawagarh Formation along Bagnotar-Baragali Section, Lesser Himalaya Northern Pakistan. Surface fracture data were collected including orientation, attitude (Dip/Strike), fracture density (F.D), frequency and their distribution. The methodology implemented comprises of surface fracture data and subsequent statistical calculations by Monte Carlo equation followed by scanline circle inventory method. The data was collected from 198 different stations with 75 fractures inventories. The statistical data is then compared with the petrography, SEM and EDX data already available. Additional, the NFRs system was classified and recognised for the studied carbonate units based on the comparative analysis. Likewise, stress analysis was integrated with the results which displays that major stresses in NW directions whereas minor stresses were acting in NEE direction. The Stereonet diagram shows that the maximum fractures are NW-SE oriented, average amount of fracture are NE-SW oriented while Minimum amount of fracture are oriented in NEE-SWW direction. The fractures direction show three sets of joints making X-shape, which indicate that these fractures are interconnected and due to which the reservoir potential can be heightened. The average Fracture Density (FD), Porosity and permeability were calculated as 0.043136, 3.212509 and 0.282299 values respectively. The X-plots of Fracture Density (FD) vs. Porosity and Permeability is weak which decrease reservoir potential while the interrelationship of Fracture Porosity and permeability is very strong which yields supposed to enhancing reservoir potential of Kawagarh formation. The analysed formations show intermediate to low porosity and permeability and classified as Type 2 or Types 3 in NFRs system based on the Visual porosity (V.P) calculated from petrography and the fracture data from the outcrop. This further shows that, the fractures provide essential permeability only in case of types 2 while in case of type 3 the fractures provide a permeability assistance. Classification of Natural Fractured Reservoir (NFR) (Nelson, 2001) Shows that Kawagarh formation is type three (Poor) reservoir. The comparative analysis also shows that Kawagarh formation has a poor reservoir potential in Qamar Mela (Nizampur Basin) and Kala Chitta Ranges.