Abstarct: Sandstone reservoirs often contain clay minerals which the type and distribution of these minerals are effective on reservoir properties. There are several methods for identifying clay minerals that X-ray diffraction (XRD) is a common method. Identification of the type, volume and distribution of clay minerals in petrophysics studies of reservoir is very crucial and it is effective in calculating porosity and permeability. Since clay minerals in reservoirs are seen as shale in reservoir formations, in a petrophysical assessment of the reservoir, it is necessary to know some important parameters of shale reservoir including gamma ray, neutron porosity, sound transmission time and the shale density which are determined from wells charts. In order to accurately assess the volume of shale and identify them, it is necessary to integrate well logging and laboratory data. In this research, the separation of clay minerals using petrophysical data is conducted by laboratory methods and interpretation of petrophysical logs. Generally, the well was studied by well log charts data and by using the Geolog software, the distribution of clay minerals was determined. Samples were also taken from different depths of the well. These specimens were examined by X-ray diffraction (XRD) and the distribution of clay minerals was also obtained in general and specialized manner. The results of the overall analysis of XRD on samples indicated the presence of dolomite, quartz, anhydrite, calcite and clay minerals in samples. The results of the special XRD analysis of the samples showed that different clay minerals, including montmorillonite, illite, kaolinite, chlorite and vermiculite, were present in selected samples. The petrophysical analysis of well data with software of Geolog 7 showed that chlorite, illite, montmorillonite minerals with interlaxyer minerals are also present in wells. Comparison of the results of two methods shows that the XRD method and the analysis of well logging graphs have close and similar results. However, the XRD method has a higher accuracy in determining the clay minerals than the well logging graphs method, so that the resolution of clay minerals in this method is higher than the analysis of well logging charts. In fact, laboratory results have been used for validation and petrophysical interpretation to improve the results of its interpretation. In order to determine the effect of clay minerals on the petrophysical properties of the studied well reservoir, including shale volume and porosity at depths of 3724 m and 3917 m, it was concluded that the presence of clay minerals (from the smectite class) as shale at a depth of 3724 meters is higher than 3917 meters in depth. In this case, petrophysical calculations show that porosity at a depth of 3724 meters is 25 percent of total porosity and at a depth of 3917 meters porosity is 80 percent of total porosity.