Petrophysical properties and hydrocarbon potentiality of Balkassar well 7 in Balkassar oilfeld, Potwar Plateau, Pakistan Syed Bilawal ali Shah* & wan haSiah aBdullah Department of Geology, University of Malaya. Kuala Lumpur, 50603, Malaysia *Corresponding author: bilawalshah22@siswa.um.edu.my Abstract: The Balkassar Oilfeld is located in the eastern Potwar sub-basin, and lies on the Soan Syncline southern fank of the Himalayan collisional regime. In this study, petrophysical properties of reservoir rock of the Chorgali Formation of Eocene age encountered in well 7 of the Balkassar Oilfeld were evaluated for reservoir rock potentiality. A set of wireline logs containing neutron, density, gamma ray, spontaneous potential and resistivity logs of well 7 from Balkassar Oilfeld were interpreted carefully to estimate porosity, water saturation and hydrocarbon saturation. The method used for this petrophysical analysis is spontaneous potential logs in calculating water resistivity followed by Archie’s equation to convert water resistivity to water saturation. Based on the petrophysical analysis performed on the Balkassar well 7, the results show that about 21.1% average porosity, 33.5% water saturation and 66.5% hydrocarbons saturation were obtained for the Chorgali Formation. Thus, this indicates that Chorgali Formation has an average to good reservoir potential. Keywords: Petrophysical analysis; Balkassar oil feld; Chorgali Formation; reservoir potential INTRODUCTION The Balkassar oilfeld is located in Potwar Plateau, within the Central part of Potwar Sub-basin that forms part of lesser Himalayan Foreland Fold and Thrust belt (Duory et al., 1989; Farah et al., 1984; Tahirkheli, 1979; Kazmi & Jan, 1997; Khan et al., 1986). The Balkassar oilfelds are one of the major oil producing felds in the region. Balkassar oilfeld is very important as it is host to proven hydrocarbon reserves (Kadri, 1995), however there is lack of information available regarding petrophysical data. As according to Kadri (1995), Ahsan et al. (2013) and Iqbal et al., (2015) the Balkassar has the potential to produce hydrocarbons. According to Aadil et al. (2014) and Khalid et al. (2015) the key to success for exploration of hydrocarbon is petrophysical analysis. Geophysical wireline logs are commonly applied to convert raw logs data into suitable information capable of providing estimation of oil and gas in the subsurface (Quijada et al., 2007). Wireline logs are very benefcial for defning the rocks characteristics such as, lithology, permeability and porosity which are the most signifcant properties of rocks in oil and gas exploration (Asquith et al., 2004). For qualitative description of reservoirs, Amigun & Odole (2013), Rider (1986) and Van Golf-Racht (1982), have reported on criteria used for porosity. Table 1 shows the criteria that has been adopted for this study. The aim of this study is to interpret wireline logs of Balkassar well 7 to evaluate hydrocarbon potential of the reservoir rock Chorgali Formation. The main objectives are to identify the lithology and to calculate porosity, water resistivity, water saturation and hydrocarbon saturation. LOCATION OF STUDY AREA The Balkassar oilfeld is located in the middle of the Potwar Plateau within the Upper Indus Basin, Punjab, Pakistan (Figure 1), and is part of the Himalayan Active Foreland Folds and Thrust Belt of northern Pakistan. Its coordinates are 32°55’ N and 72°39’ E. The location of Balkassar well 7 is shown in Figure 1b. MATERIAL AND METHODS This study uses one well, that is Balkassar 7 for investigation of Eocene reservoir rock of Chorgali Formation to evaluate its hydrocarbons potentiality. The well logs data for this study was provided by the Directorate General Petroleum Concessions (DGPC), Islamabad Pakistan. Petrophysical analysis The method used in this study was adopted from Zahid et al. (2014), Mehmood et al. (2015) and Hartmann & Beaumont (1999). The petrophysical analysis based on wireline logs (Gamma Ray, Neutron, Density, Resistivity, and Spontaneous-potential) for Eocene age Chorgali Formation encountered in the Balkassar well 7 was conducted. The analysis were made to calculate porosity, formation water resistivity, water saturation and hydrocarbon saturation. All of these parameters are very useful in investigating the reservoir hydrocarbon potential. Table 1: Criteria set by Rider (1986), for qualitative description of reservoir adopted for this study. Qualitatively Evaluation of Porosity Average Porosity Qualitative description 0-5 Negligible 5-10 Poor 10-20 Good 20-30 Very Good >30 Excellent Bulletin of the Geological Society of Malaysia, Volume 62, December 2016, pp. 73 – 77