Electromagnetic mixing rules of the type developed by Maxwell Garnett, Bruggeman, and the Coherent Potential formula are shown to be useful for evaluation of the porosity (or cementation) exponent, m, in naturally fractured reservoirs represented by dual and triple porosity models. Comparisons are made with core data from limestone, dolomite and tight gas reservoirs to corroborate results from the theoretical models.

Rigorous values of m reduce the uncertainty in calculated values of water saturation and hence improve estimates of hydrocarbons-in-place and recoveries particularly in situations where sufficient data are not available to utilize the material balance approach.

The main advantage of the new method developed in this paper for petrophysical analysis is that it can handle with the use of one single equation the individual mixing rules mentioned above, and at the same time quantify values of matrix, fracture and non- connected vug porosity, and the cementation exponent of the total porosity system.

It is concluded that electromagnetic mixing rules provide a useful methodology for petrophysical evaluation of complex dual and triple porosity reservoirs.

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