Reservoir characterization is a process of describing various reservoir characteristics using all the variable data to provide reliable reservoir models for obtaining an accurate reservoir performance prediction. Reservoir characterization plays a crucial role in modern reservoir management. The reservoir characteristics include pore and grain size distribution, permeability, porosity, facies distribution, and depositional environment. The types of data need to describe the characteristics are core data, well logs, well tests and seismic reflection data. Permeability and rock type (i.e. lithology, pore geometry and range of porosity and permeability) are the most important rock properties which can be used as input parameters to build a 3D petrophysical model of the hydrocarbon reservoir. These parameters are derived from core samples which may not be available for all boreholes, whereas almost all boreholes have well log data.