30 htp://jpst.ripi.ir Journal of Petroleum Science and Technology 2018, 8(3), 30-41 © 2018 Research Insttute of Petroleum Industry (RIPI) ABSTRACT Despite advancements in specifying 3D internal microstructure of reservoir rocks, identfying some sensitve phenomenons are stll problematc partcularly due to image resoluton limitaton. Discretzaton study on such CT-scan data always has encountered with such conficts that the original data do not fully describe the real porous media. As an alternatve atractve approach, one can reconstruct porous media to generate pore space representatons. The reconstructed structures are then used for simulatons using some sort of discretzaton. In this paper, It is examined the efect of discretzaton on porosity and saturaton calculatons in porous media models. Some 3D Boolean models of random overlapping spheres of fxed and variable diameters in three dimensions are used. The generated models are then discretzed over 3D grids with diferent number of voxels. The porosity can be calculated and saturaton of the discretzed models are then compared with the analytcal solutons. The results show that when meshgrid sizes are 8% of smallest grains, porosity is calculated with 95% precision. In additon to that, meshgrid sizes of 5% and 3% of average grain diameter are adequate to calculate non-wetng and wetng phase saturatons with at least 95% precision. This helps in choosing the optmum voxel size required in imaging for efciently use of available computatonal facility. Keywords: Boolean Model, Discretzaton, Micro-CT, Mesh-Grid, Model Porous Media, Porosity, Saturaton Ahmed Zoeir* 1 and Jafar Qajar 2 1 Faculty of Petroleum and Natural Gas Engineering, Sahand University of Technology, Tabriz, Iran 2 School of Chemical and Petroleum Engineering, Shiraz University, Shiraz, Iran To Express Required CT-Scan Resolution for Porosity and Saturation Calculations in Terms of Average Grain Sizes *Corresponding author Ahmed Zoeir Email: ah_zoeir@sut.ac.ir Tel: +98 938 4508088 Fax: +98 71 36133753 Artcle history Received: April 1, 2017 Received in revised form: September 20, 2017 Accepted: September 26, 2017 Available online: July 15, 2018 DOI: 10.22078/jpst.2017.2620.1443 Journal of Petroleum Science and Technology INTRODUCTION The characterizaton of the microstructure of natural and synthetc porous materials has been of great importance for scientsts and engineers over a wide range of disciplines and hence, it has been the subject of numerous studies in various felds. In petroleum engineering, for example, an understanding of the interactons among rock microstructure, mineralogy, and fuids in pore space is crucial to us for beter interpretaton and predicton of reservoir rock propertes and fow processes in underground formatons. Development in structural study of porous materials has a long history. Over the past two decades, direct measurements of 3D structures at resolutons down to a few microns using X-ray micro-