Rock permeability is one of most important rock properties for fluid flow in reservoir. According to Darcy’s law flow rate is proportional to permeability holding other variables constant. The methods to get permeability include direct core measurement, well test interpretation, estimating from nuclear magnetic resonance (NMR) logs, and calculating from other properties such as porosity using correlations. It is noted that these methods have their own limitations. Core measurement is expensive, time consuming and limited by core availability. NMR logs are high cost. Correlations are often obtained from scatter data point thus their reliabilities cannot be guaranteed. Therefore new method needs to be found to get permeability.

Starting from multiple-capillary tubes concept, we derived a rigorous relationship between permeability and formation resistivity factor. Through this correlation permeability can be calculated from known formation resistivity factor or vice versa. Since formation resistivity factor is often obtained from lab experiment, the new correlation provided an important supplement in permeability estimation without additional cost. In other words, if permeability is known, the new correlation can be used to verify the formation resistivity factor measured from lab experiment, again, without adding cost. The new correlation also provides a unique approach to quantify the radius of capillary tube, which is not available in the literature before this study.

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