Identification of hydraulic flow units (HFUs) is an important part of reservoir characterization. Rock samples within a given HFU are expected to have the same mean hydraulic radius. We show that the famous reservoir quality index-flow zone indicator (RQI/FZI) technique and its recent modifications do not use the concept of mean hydraulic radius. Each predicted HFU by these methods may contain the samples with different pore structures, and further the rocks with similar structures may be distributed in more than one HFU. This makes the reservoir characterization very complicated and sometimes an erroneous process. An improved method, referred to as FZI star method (FZI*), is presented here using the base form of the Kozeny-Carmen (K-C) equation, opposed to RQI/FZI method which relies on the generalized form of the K-C equation, by proper consideration of the mean hydraulic radius concept. The presented method is verified using a large set of capillary pressure measurements.
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