Facies and Hydrocarbon Reservoir Rock Characterization of the Paleozoic Rocks of Peshawar Basin, Northwest Pakistan

Abstract

The present study details the facies description and hydrocarbon reservoir characterization of the Paleozoic rocks of Peshawar Basin, northwest Pakistan. The outcrop samples from the Cambrian-Devonian rocks along the famous Nowshera-Risalpur Road and Turlandi Village Section were investigated. The analysis of outcrop data revealed significant information regarding the facies and their depositional environments. Based on its detailed sedimentological data, it is believed that the Ambar Formation is deposited in shallow shelf-tidal flat settings, while the protolith of the Misri Banda Quartzite came from the wide beaches. The protolith of the Panjpir Formation was deposited in the shelf conditions, which shows an overall shallowing when moving up the section from the argillites and phyllites to crinoidal limestone. The Nowshera Formation was deposited as a reef complex on the shelf edge having reef core, reef breccia and a back-reef lagoon. The techniques of petrography, XRD and SEM were used for the bulk geochemical composition of the rocks focusing on their matrix, mineralogy, micro-porosity and pore-filling materials. The presence of micrite, goethite, kaolinite and illite as intergranular mass, dolomitization-induced porosity, twin cleavage plane and high dissolution porosity in the Ambar Formation can provide significant pore space to the reservoir fluids migration. Hematite with minor kaolinite, illite and chlorite as alteration products of unstable framework grains as intergranular mass and a deep seated burial diagenesis has minimized the reservoir potential in Misri Banda Quartzite. The coarse and fine calcite, dolomite, chlorite and kaolinite occur as pore-filling material between the framework grains while the high intensity of intragranular dissolution and micro intergranular connecting porosity in the Nowshera Formation makes it a promising reservoir.