Characterization of carbonate reservoir is still a big challenge as compared to sandstone reservoir. One of the best way to manage heterogeneity, is subsurface model. To modelling, discretized the formation into a few layers, that each layer having similar petrophysical properties. Core samples and log data can be important as the first information, which can be obtained after reservoir exploration. To increase the accuracy of the model, the optimal number of Hydraulic flow units should be achieve. HFU is a volume of rock within a reservoir, that has petrophysical and lithological attributes that affect flow properties and differ from those of surrounding units. The studied samples subjected to permeability and porosity measurements and differentiated into different HFUs. Histogram analysis, normal probability plot were used to determine optimum number of HFUs in the one of Iranian gas fields. After examination, six HFUs were identified, that HFU-4 and 5 were identified as the best reservoir zone.

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