FACIES ANALYSIS AND RESERVOIR CHARACTERIZATION OF THE OUTCROP ANALOGUE AND WELL DATA, SHINAWARI FORMATION (MIDDLE JURASSIC) IN THE NIZAMPUR AND KOHAT BASIN (KPK), PAKISTAN

Abstract

The present study deals with the facies analysis and reservoir characterization of the outcrop analogue and well data of Shinawari Formation (middle Jurassic) in Nizampur and Kohat Basins (KPK) Pakistan. Nizampur Basin is located in the north of Kala Chitta Range whereas Kohat Basin is located on west of Kala Chitta Range. Shinawari Formation in the study area mainly composed of limestone, marl, silt/sand and shale. Thin section petrographic and paleoenvironmental study was done and subsequently used in the microfacies analysis. Five microfacies were identified in three depositional environments, which included peritidal, restricted lagoon and high-energy shoal from inner to outer part of a homoclinal carbonate ramp. The analysis was based on (Flügel, 2004) model for ramps and facies assessments. The wire line logs data of wells (Manzali-01, Manzali-02 and Makori-01) from Kohat Basin was used for petrophysical studies and four limestone electrofacies were identified. These facies were vacillated from clean limestone to marly/argillaceous limestone, which were sandwiched by dominant shale and traces of silt/sandstone in places. Lithological correlation showed that limestone facies were slightly pinched out from north east to south west direction, with gamma ray (GR) values between 30 to 70 API. The results of wire line logs showed no hydrocarbons presence in Shinawari Formation in Manzalai-1 and Manzalai-2 wells. However, the logs were encouraging in the Makori-1 well, clean limestone was developed in the upper most part of Shinawari Formation and having considerable porosities from 1.5% to 4.5%. The wire line logs data represented the Shinawari Formation having good reservoir qualities in the eastern side of the Kohat Basin whereas the western part of the basin is less prospective. Therefore, it is not a potential target in the wells located in the western side of the Kohat Basin. Whereas the study area of Nizampur Basin is located toward north eastern side of the Kohat Basin, thin section studies showed the presence of dolomitization and other porosity behaviours which may indicate the development of secondary porosities. Based on available data interpretation Shinawari Formation can be consider as a potential future exploration target in the Nizampur Basin.