Petrophysical data are one of the important tools for evaluating hydrocarbon reservoirs. In many cases a complete set of logs may not be available. Well conditions, defective logging tools, data loss due to unsuitable maintenance and incomplete logging are some of these reasons. In this research, a fuzzy system has been introduced and used to estimate the size of openings and fracture densities from wellbore data. In this method, by merging the input data and an output data obtained in the previous step, (using 8 .GEOLOG), a fuzzy system is created using the MATLAB software, and then by recalculating the output data (openness, density), using a different method and the results are compared with each other. The data set of this study is related to Sarvak Formation with Albin-Cenomanian age in two wells from one of the southwest oil fields.