Irreducible water volume from the new Magnetic Resonance (MR) logging tools provides the log analyst with insight into a formation?s permeability and its water-cut potential. However, the traditional T2 cutoff method to determine the bulk volume of irreducible water (BVI), currently in wide use, has been found to be inadequate for some formations and fluid conditions. A new method to characterize bulk volume irreducible that addresses these issues is presented in this paper. The method is based on the premise that each pore size has its own inherent irreducible water saturation. Given that relaxation time is related to pore size, this method utilizes core MR measurements to relate each relaxation time to a specific fraction of capillary bound water. Thus, the bulk volume irreducible becomes a direct output of the inversion of the echo data, and it utilizes the entire T2 distribution. Core data are presented that demonstrate the Spectral Bulk Volume Irreducible (SBVI) petrophysical model and the method used for its characterization. Log examples of the SBVI implementation are presented to demonstrate the improvements brought by this development.

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